High strength epoxy adhesive and uses thereof

ABSTRACT

An epoxy composition effective for forming a thermally curable structural adhesive, and in particular, a two part epoxy resin composition that when cured can obtain preferred and improved physical and chemical characteristics useful in structural assembly applications.

[0001] The present application is a divisional of U.S. patentapplication Ser. No. 09/170,597, filed on Oct. 13, 1998.

FIELD OF THE INVENTION

[0002] The invention relates to epoxy resin compositions, particularly,to an epoxy resin composition that when cured exhibits properties usefulin structural assembly and, even more particularly, to two-part epoxyadhesive compositions that exhibit one or more improved adhesiveproperties such as impact, creep and fatigue resistance, as well asdurability under service conditions for structural applications.

BACKGROUND OF THE INVENTION

[0003] Adhesives have been used in many structural applications. Suchstructural applications have included vehicles, computer cases,buildings, appliances, etc. For example, structural adhesives have beenused in vehicle assembly (e.g., automobile and aircraft assembly) toreplace or augment conventional joining techniques such as welds, nutsand bolts, and rivets.

[0004] Epoxy compositions are known and have been used for structuraladhesive applications. In state-of-the-art epoxy technology today,polymerization catalysts used to achieve higher order oligomerstypically are tetraalkyl ammonium or phosphonium salts that do notpromote epoxy homopolymerization. Cyclic amidine catalysts, such asimidazoline catalysts and imidazole catalysts, have also been used inadhesives. The adhesives of the prior art are quality adhesives in manyapplications. Even so, there is a continuing need for higher performanceadhesives in order to meet the changing needs of various industries suchas, for example, the vehicle assembly industry.

SUMMARY OF THE INVENTION

[0005] The present invention is intended, at least in part, to addressthe ongoing need for higher performance adhesives to meet the needs ofvarious industries, including the vehicle assembly industry (e.g.,automobile, aircraft and watercraft industry). Compositions of theinvention are believed to be useful in structural adhesive applicationseither alone or in conjunction with conventional assembly techniqueslike welding and/or mechanical fastening (e.g., rivets).

[0006] We have found a composition useful as a structural adhesivehaving long term durability under static and/or dynamic loads andsubstantially improved impact, creep and/or fatigue resistance for usein assembly applications. The composition can include a chain extender,a catalyst, a reactive epoxy resin and one or more polymeric tougheners.At least when mixed together, the present adhesive composition is in aform that can be applied or dispensed (e.g., liquid or paste form). Thechain extender, the reactive epoxy resin, the catalyst and the toughenerare each in an amount and of a type that are effective, when mixedtogether, to form a thermally curable adhesive. When the adhesive iscured, at least about 50% by weight of the epoxy resin is chainextended. Preferably, at least 60 wt %, and even more preferably atleast 70 wt %, of the epoxy resin is chain extended.

[0007] It is preferred that the composition be free, or at leastsubstantially free, of a polyfunctional curing agent (i.e., an agentthat chain extends and cross links the epoxy resin). That is, the amountof polyfunctional curing agent should be limited to the point that, whenthe adhesive is cured, the desired amount of the epoxy resin is chainextended.

[0008] The chain extender can comprise an amine, a phenolic compound ora combination thereof. Preferably, the chain extender is all or at leastsubstantially in monomeric form (i.e., the chain extender is notprereacted, prepolymerized or in oligomeric form) prior to being addedto the composition. That is, enough of the chain extender is inmonomeric form to enable the resulting composition to be applied ordispensed. Preferably, the resulting composition is compatible withstate-of-the-art dispensing and rheology (e.g., viscosity) requirements.It is also preferable that the chain extender be dissolvable into theepoxy resin, the catalyst or both, at least at an elevated temperature(e.g., the curing temperature of the composition). It may be desirablefor the chain extender to be in solid particulate form and finelydispersed in the epoxy resin and/or the catalyst, where the chainextender dissolves at elevated temperatures.

[0009] The phenolic compound preferably includes a dihydric phenol(e.g., a di-hydroxy benzene, such as catechol, resorcinol and/orcompounds based thereon), and the amine preferably includes a primarymonoamine (e.g., attached to a primary or secondary carbon), a secondarydiamine, and compounds based thereon. A polyfunctional ormultifunctional amine (e.g., a diamine containing both primary andsecondary functionality or multiple primary functionality) will causechain extending and cross linking (i.e., will function as a curingagent). Even though it will cause cross linking to occur, apolyfunctional amine or other curing agent may be used, but in a limitedamount.

[0010] The present composition can be a two-part adhesive with thecatalyst in a part A and the reactive epoxy resin in a part B. The chainextender is included in at least one of the two parts. When the chainextender of such a two-part adhesive composition includes an amine, theamine is preferably only in the part A. It may be possible to add verysmall amounts of amine in the epoxy part B, as long as the amount ofamine is not enough to adversely affect the part B (e.g., its rheology).When the chain extender of such a two-part composition includes acatechol, the catechol can be in the part A, in the part B or in both.It is preferable that the catechol is in at least the part A. It issurprising that the catechol can be sufficiently stable (i.e., notrecrystalize or react) in the epoxy resin to provide a part B with acommercially acceptable shelf life. When the chain extender includes acatechol and resorcinol, at least the part A includes the resorcinol andcatechol. The part B can include the catechol without resorcinol. Whenthe chain extender includes another type of phenolic compound, it mayalso be included in the part A, part B or both.

[0011] It can be preferable for at least about 50 wt % of the chainextender to be catechol. When such a chain extender also includesresorcinol, up to about 50 wt % of the chain extender can be resorcinol.It is believed that the adhesive composition can contain in the range offrom about 8 wt % to about 30 wt % of such a catechol and resorcinolcontaining chain extender, based on the amount of chain extender andreactive epoxy.

[0012] The catalyst is preferably a base. The catalyst can include acyclic amidine, a tertiary amine, and substituted analogues thereof. Thecatalyst can comprise one or more of imidazole, imidazoline, asubstituted imidazole compound, a substituted imidazoline compound,1,4,5,6-tetrahydropyrimidine, a substituted 1,4,5,6-tetrahydropyrimidinecompound and combinations thereof. The chain extender preferablyincludes catechol. The catalyst can also include one or more substitutedpyridines, pyrrolidines and piperidines. The chosen catalyst orcatalysts should not contain a group that exhibits an electronwithdrawing or stereo chemical effect sufficient to prevent thecomposition, when mixed together, from forming a thermally curableadhesive suitable for structural bonding. Typically, as the mass of thecatalyst increases, the amount of catalyst needed to establish a desiredeffect also increases, unless any substitution chemistry present has anaffect on (i.e., increases or decreases) the effectiveness of thecatalyst. The catalyst can comprise two or more different catalysts. Wehave surprisingly found that a combination of two different amidinecatalyst species, in particular cyclic amidine catalysts, can provideenhanced adhesive properties. A preferred combination can include one ormore imidazole compounds (substituted or unsubstituted) and one or moreimidazoline compounds (substituted or unsubstituted). It is believedthat a combination of a 1,4,5,6-tetrahydropyrimidine compound(substituted or unsubstituted) with an imidazoline compound and/or animidazole compound may also provide enhance adhesive properties.

[0013] Preferably, the amount of the catalyst in the adhesivecomposition is at a level of at least about 0.5 wt-%, more preferably,in the range of from about 0.5 wt-% to about 10 wt-% or, even morepreferably, in the range of from about 0.5 wt-% to about 7.5 wt-%, basedon the total amount of the reactive species or components of theadhesive mass (i.e., the chain extender, epoxy resin and catalyst) andthe molecular weight of the catalyst.

[0014] The reactive epoxy resin can comprise one or more glycidyl etherepoxy compounds, each having more than one reactive epoxy group.Preferably, the reactive epoxy resin comprises at least one of anaromatic glycidyl ether epoxy compound and an aliphatic glycidyl etherepoxy compound, with at least one compound having more than one reactiveepoxy group. Typically, the reactive epoxy resin materials are presentin amounts in the range of from about 50 wt-% to about 90 wt-%, andpreferably about 80 wt-%, based on the reactive species of thecomposition (i.e., catalyst, chain extender and epoxy).

[0015] It is desirable for the adhesive composition to contain up to 35parts, preferably in the range of from about 5 parts to about 35 parts,and more preferably from about 10 parts to about 30 parts, by weight ofpolymeric toughener based on 100 parts by weight of the reactive epoxyresin. For a two-part adhesive composition of the present invention, thetoughener can be added to the part A, the part B or both.

[0016] The present adhesives may be used to supplement or completelyeliminate a weld or mechanical fastener by applying an adhesive massbetween two parts to be joined and curing the adhesive to form a bondedjoint. Optionally, spot welding can be used to pin the parts togetheruntil the adhesive is sufficiently cured for handling. Welding cancontribute to the curing process. The adhesives may be used to formassembled structures by applying the adhesives to augment or replacewelded joints and other mechanical joints. Replacing or supplementingwelded joints with an adhesive bond to create a load bearing joint isbelieved to require superior adhesive toughness over a broad temperaturerange in some applications, as well as adequate adhesion to thesubstrates being bonded. This is related directly to the degree ofpolymeric matrix ductility, which requires chain extension allowing foroptimum toughening. Compatibility with state-of-the-art dispensing andrheology (e.g., viscosity) requirements for a flowable one- or two-partadhesive composition can require this chain extension to occur, at leastsubstantially if not completely, after the adhesive is applied.

[0017] For the purposes of this patent application, the term “activehydrogen” denotes a hydrogen atom in a chemical group wherein the groupbecomes chemically reactive with the oxirane group resulting in ringopening bonding to the group. Active hydrogens typically are found inamines, thiols, carboxylic acids and phenolics. Preferred activehydrogen groups include amine (—NH—, —NH₂) groups and aromatic hydroxyl(—OH) groups. The function of the active hydrogen compound is to providechain extension. Some cross-linking can be introduced by polyfunctionalamines but only to a limited extent. If excessive cross-linking occursthe adhesive can lose toughness and adhesion. Conversely excessive chainextension with little epoxy homopolymerization will result in a weakadhesive.

[0018] The first part or part A of the two-part epoxy adhesive comprisesthe catalyst. The second part or part B comprises the reactive epoxyportion and optional toughener. One formulation places dihydroxyphenolic in the epoxy part B with only the catalyst in a part A. Asecond formulation places the amine and/or dihydric phenol along withthe catalyst in the part A and the epoxy and a toughener in the part B.A third formulation places a portion of the phenolic in both the part A(catalyst) and part B (epoxy).

[0019] In the adhesive of the invention, we have found that thestoichiometric equivalents ratio of reactive hydrogen sites to reactiveepoxy sites is preferably less than 1.0 (i.e., for each epoxy equivalentin the adhesive, there is less than 1.0 equivalents of active hydrogen).We have also found that it can be preferable for the stoichiometricequivalents ratio to be in the range of from about 0.5 to less than 1.0,in the range of from about 0.6 to less than 1.0, or in the range of fromabout 0.7 to less than 1.0. The active hydrogen sites can be provided bythe chain extender and catalyst. Fillers or the toughener can beindependently incorporated in either or both parts A or B. We have foundthat an amine of the type described above can replace a portion of thedihydric phenol without a loss in physical properties and may be usefulas the only chain extender in the composition. The amine can act as adiluent for the Part A, to lower its viscosity, but may also shorten thework-life of the mixed adhesive. Another function of the amine is toreduce any tendency of the phenolic to recrystallize and help stabilizethe viscosity of the Part A. A further function is providing latitude informulating for a specific volumetric mix ratio to meet dispensingrequirements.

[0020] Adhesives made using the formulations of this invention canobtain an impact peel strength of at least about 3 Joules, preferably atleast about 5 Joules and most preferably at least about 10 Joules at atemperature in the range of from about −40° C. to about 90° C. Thedesirable impact peel strength depends, at least in part, on the type ofsubstrates being adhered together. Further, adhesives according to thepresent invention can form adhesive bonds having a T-peel strength ofgreater than about 70 N/cm width at 23° C., greater than about 85 N/cmwidth at 23° C., and greater than about 100 N/cm width at 23° C. Theadhesive can sustain a load under certain accelerated environmentalcycling conditions for at least 10 days, preferably greater than 20days, most preferably greater than 30 days.

[0021] In another aspect of the present invention, a structure isprovided that has a first surface and a second surface joined by anadhesive bond made with a cured mass of the above described adhesivecomposition. The structural adhesives of the invention can form highquality adhesive bonds between metallic components (e.g., iron,aluminum, titanium, magnesium, copper, etc. and alloys thereof), betweennon-metallic substrates (e.g., reinforced and unreinforced thermoplasticand thermoset polymers, as well as other organic materials or organiccomposite materials) and between metallic and non-metallic substrates.The structure being bonded can form at least a portion of a vehicle.

[0022] We have also found that adhesives used to augment or replace weldconstruction can provide useful properties to an assembly. Weldedjoints, while strong, tend to concentrate stress at the weld nuggetperimeter and can fail at the weld perimeter if sufficient impact energyis applied to the joint. Additionally, corrosion resistance associatedwith the weld nugget and adjacent metal is typically reduced. Curedepoxy adhesives of the present invention can absorb substantial impactenergy and dissipate the energy throughout the structure. Such energydissipation properties, in conjunction with weld joints, can improve thesurvivability of a structure under conditions of high impact loads. Suchan adhesive requires significant structural properties. Regardless ofthe direction of the impact energy, it may be desirable for the adhesivemass to be able to maintain structural integrity regardless of whetherthe adhesive is exposed to stress in a cleavage mode, a shear mode, acompression mode or a tensile mode. Therefore, the structure cancomprise a joint having a welded bond in addition to the adhesive bond.In addition, the welded bond can be formed through the adhesive bond.

[0023] We have found two characteristics of adhesives that can helpidentify an adhesive that is useful in this type of application. We havefound that the impact peel strength and T-peel adhesion of the adhesivecan be useful indicators for adhesive utility. Other characteristics ofadhesives useful as performance indicators can also include sustainedload durability and fatigue resistance. The epoxy adhesives of theinvention may be used in a structure having structural integrity that ismaintained with both welded joints and adhesive bonds made using thecurable adhesive of the invention or with only such adhesive bonds.Adhesives are also desirable, for example in the automotive industry,because in an effort to reduce weight, car manufacturers are looking touse thinner gauge steel either alone or in combination with aluminum,magnesium, etc. In addition, the present adhesives can be a viableoption for bonding together various organic materials or compositeswhich cannot be welded or joined with conventional methods. Additionalbenefits of a structure bonded according to the invention are believedto include improved crash worthiness (i.e., impact resistance),survivability, corrosion resistance, sealing of the joint and vibrationdamping.

[0024] In an additional aspect of the present invention, a method isprovided for assembling the above described adhesively bonded structure.The method comprises the steps of: (a) applying an uncured mass of thecomposition of claim 1 to at least one of a first member and a secondmember; (b) sandwiching the uncured mass between the first member andthe second member; and (c) curing the composition to form an adhesivebond so as to adhere the first member and the second member together.The first member can be a frame member and the second member can be asheet-like member or another frame member. The method can also includethe step of welding the sheet-like member to the frame member throughthe uncured mass before the curing step.

[0025] Adhesives can be used for such applications, but known structuraladhesives that are currently available for such applications do not havethe requisite combination of properties and performance over typical enduse (e.g. service) temperature ranges. Such properties include long termdurability and fatigue resistance under static and dynamic (e.g. cyclic)loads and good impact resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIGS. 1-5 show the test device and test specimen used todetermine impact peel strength. FIGS. 1 and 2 show the test wedge usedin the test. FIGS. 3-5 show the test specimen configured for the test,its installation on the wedge and the specimen after application of thetest force.

[0027]FIG. 6 shows an assembly comprising a hydroformed tubestructurally assembled with and adhered to a panel using the adhesive ofthe invention. This assembly structure includes means that maintain thestructure and position during adhesive curing.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0028] The two part epoxy adhesive compositions of the present inventioncomprise a catalyst part A (e.g., a cyclic amidine) and an epoxy part B.Either the part A, part B or both will also contain a chain extender anda toughener. The novel compositions of the invention provide ductile andtough structural adhesives that have good long term durability andfatigue resistance under static loads and dynamic loads. The resincompositions of the invention are believed especially useful asstructural adhesives where the operating temperature of the bondedarticle or material is expected to be substantially above and/or belowroom temperature, such as the range of service temperatures typicallyseen by a vehicle (e.g., automobiles, aircraft and watercraft). Thepresent epoxy adhesives, when cured, are believed be useful attemperatures in the range of from about −40° C. to about 90° C. and,more desirably, from about −40° C. to about 120° C. Additionally, whenused to join together parts of the frames of vehicle bodies, theadhesives can stiffen the joints and thus stiffen the vehicle'sstructure, as well as impart sealing and/or vibration damping propertiesto the vehicle bodies.

[0029] Preferred adhesive compositions of the present invention cancomprise a glycidyl ether type epoxy, an amine (e.g., a primarymonoamine and/or secondary diamine) and/or a dihydric phenol, a cyclicamidine catalyst, and a toughening agent, in which the epoxy and chainextender (i.e., amine and/or dihydric phenol) are substantiallyunreacted before the composition is exposed to a catalyst to cure theadhesive.

[0030] Another embodiment includes a two-part epoxy compositioncomprising a Part A or first part having a cyclic amidine catalyst, anda Part B or second part comprising an epoxy, a dihydric phenol andtoughening agent wherein the epoxy and dihydric phenol are substantiallyunreacted, and a two-part epoxy composition comprising Part A having acyclic amidine catalyst and catechol (i.e., 1,2-dihydroxybenezene), anda Part B comprising epoxy and toughening agent where a portion of thedihydric phenol can also be incorporated in Part B. A third embodimentcomprises a Part A having a cyclic amidine catalyst, dihydric phenol andan amine (i.e., a primary monoamine and/or secondary diamine), and aPart B comprising epoxy and toughener. In all of these compositionsfillers can be incorporated in both parts A and B. The amount (wt-%) ofPart A and Part B can be substantially varied by the amount of fillerused and the composition of each Part.

[0031] The two part epoxy adhesive compositions of the invention containdihydric phenol. Suitable dihydric phenolic compounds of the inventioninclude bisphenols (e.g., Bisphenol A, Bisphenol F, etc.)dihydroxynaphthalenes and dihydroxybenzenes. These dihydric phenoliccompounds may be substituted or non-substituted. For example, suitablebisphenols and dihydroxybenzenes may include those that are alkyl,halogen or alkoxy substituted. Suitable dihydroxybenzenes arerepresented by the following formula:

[0032] wherein the hydroxyl groups can be ortho or meta on the aromaticring and R represents one, two or more typical substituents. In theabove formula R represents any useful ring substituent includinghydrogen. Included in these categories are 1,2 dihydroxybenzene(catechol), 1,2 dihydroxy-4-methyl-benzene, 4-t-butylcatechol, and1,3-dihydroxybenzene (resorcinol), 3-methoxy-catechol and others. It isbelieved undesirable to have bulky substituents that can causesignificant steric hindrance adjacent to the phenolic hydroxyls.

[0033] Preferred dihydric phenols include those which have hydroxylgroups attached to adjacent carbon atoms on the aromatic ring, andsubstituted analogues of these compounds. Preferred compounds includecatechol, 3-methoxycatechol, 3-methylcatechol, 3-fluorocatechol,4-methylcatechol and blends thereof. Preferably, the dihydric phenol iscatechol, or a blend of catechol and one or more other dihydric phenols.For a blend of dihydric phenols, satisfactory results have been obtainedwith the catechol being present in an amount of at least about 50percent by weight (wt-%) of the total dihydric phenol amount. We havefound that these compounds are particularly useful in forming the highstructural strength two part epoxy adhesives of the invention.

[0034] The epoxides that are useful in the composition of the presentinvention are of the glycidyl ether type. Preferred epoxides includeglycidyl ethers of Bisphenol A and F; aliphatic or cycloaliphatic diols.Useful materials can include those having a molecular weight in therange of from about 170 to about 10,000, and preferably from about 200to about 3,000. Useful materials can include linear polymeric epoxideshaving terminal epoxy groups (e.g., a diglycidyl ether of apolyoxyalkylene glycol. Useful epoxides can include those having thegeneral formula:

[0035] wherein: R′ is alkyl, alkyl ether, or aryl, preferably aryl, andn is greater than 1 or in the range of from 1 to 4. Aromatic glydicylethers can be preferred, such as those prepared by reacting a dihydricphenol with an excess of epichlorohydrin. Examples of useful dihydricphenols include resorcinol, catechol, hydroquinone, and the polynuclearphenols including p,p′-dihydroxydibenzyl, p,p′-dihydroxydiphenyl,p,p′-dihydroxyphenyl sulfone, p,p′-dihydroxybenzophenone,2,2′-dihydroxy-1,1-dinaphthylmethane, and the 2,2′, 2,3′, 2,4′, 3,3′,3,4′, and 4,4′ isomers of dihydroxydiphenylmethane,dihydroxydiphenyldimethylmethane, dihydroxydiphenylethylmethylmethane,dihydroxydiphenylmethylpropylmethane,dihydroxydiphenylethylphenylmethane,dihydroxydiphenylpropylphenylmethane,dihydroxydiphenylbutylphenylmethane, dihydroxydiphenyltolylethane,dihydroxydiphenyltolylmethylmethane,dihydroxydiphenyldicyclohexylmethane, and dihydroxydiphenylcyclohexane.Examples of commercially available aromatic and aliphatic epoxidesuseful in the invention include diglycidyl ethers of bisphenol A (e.g.,those available under the trademarks Epon 828, Epon 1001, Epon 1310 andEpon 1510 from Shell Chemical Co., and DER-331,DER-332, and DER-334available from Dow Chemical Co.); diglycidyl ethers of bisphenol F(e.g., Epiclon TM830 available from Dainippon Ink and Chemicals, Inc.);silicone resins containing diglycidyl epoxy functionality; flameretardant epoxy resins (e.g., DER 580, a brominated bisphenol type epoxyresin available from Dow Chemical Co.); 1,4-dimethanol cyclohexyldiglycidyl ether and 1,4-butanediol diglycidyl ethers. In some casesreactive diluents may be added to control the flow characteristics ofthe adhesive composition. Suitable diluents can have at least onereactive terminal end portion and, preferably, a saturated orunsaturated cyclic backbone. Preferred reactive terminal ether portionsinclude glycidyl ether. Examples of suitable diluents include thediglycidyl ether of resorcinol, diglycidyl ether of cyclohexanedimethanol, diglycidyl ether of neopentyl glycol, triglycidyl ether oftrimethylolpropane. A commercially available reactive diluent isReactive Diluent “107” from Shell Chemical Company.

[0036] The components of the composition can be present in amounts suchthat the stoichiometric equivalents ratio of reactive hydrogen sites toreactive epoxy sites is less than 1.0, in the range of from about 0.5 toless than 1.0, from about 0.6 to less than 1.0, and from about 0.7 toless than 1.0. The equivalents ratio is defined as the number ofequivalents of reactive hydrogen sites divided by the number ofequivalents of reactive epoxide sites. The active hydrogen sites caninclude the chain extender phenolic —OH, the chain extender amine —NH or—NH2, the catalyst amine —NH or combinations thereof.

[0037] We have found that the present epoxy compositions can becatalyzed with an amidine catalyst or a blend of two or more differentamidine catalysts. The preferred catalysts include cyclic amidines(e.g., an imidazole, imidazoline and 1,4,5,6-tetrahydropyrimidine) andsubstituted analogs of cyclic amidines. An amidine is generally definedas the group —N═C—N—. Suitable ring substituents for a cyclic amidinecatalyst can include a substituent such as methyl, ethyl, isopropyl,cyanoethyl, acetyl, carboxamide, methylol, etc. (e.g., for an imidazole,imidazoline or 1,4,5,6-tetrahydropyrimidine compound). The secondarynitrogen on these catalyst compounds can be further substituted as well(e.g., 1-acetylimidazole).

[0038] The preferred catalysts can include substituted imidazolines,substituted 1,4,5,6-tetrahydropyrimidines, and blends of one or both ofan imidazoline and a 1,4,5,6-tetrahydropyrimidine with another amidinecatalyst (e.g., imidazole or a substituted imidazole). Preferably, atleast the imidazoline and the imidazole catalysts do not contain anelectron withdrawing group (e.g., phenyl, nitro, carbonyl or halogen) ontheir respective ring. It is believed preferable for the ring of1,4,5,6-tetrahydropyrimidine and other amidine catalysts to also be freeof an electron withdrawing group. Even so, some degree of electronwithdrawing can be acceptable in certain positions on the ring.Preferred substituents can include aliphatic groups in the 2-positionsuch as the following 2-ethyl-4-methyl-imidazoline:

[0039] Other preferred substituents can include aliphatic groups in the1- and 2-positions such as 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine.

[0040] In the preferred practice of the invention, the amount ofcatalyst or blend thereof, is selected to provide a cured epoxy adhesivehaving unexpected properties such as sustained load durability andimpact resistance, preferably over a wide range of temperatures. It hasbeen found that the amount of catalyst used can provide the necessarybalance of epoxy homopolymerization and copolymerization with amineand/or dihydric phenol (e.g., catechol) to provide the properties neededfor both low and high temperature performance. The preferred amounts ofcatalyst can vary depending upon the catalyst type and activehydrogen/epoxy ratio (NH,OH/Epoxy ratio). The useful range needs to behigh enough to effect both the epoxy copolymerization andhomopolymerization reaction. A level of catalyst too low or too highwill result in a weak adhesive leading to poor performance. The optimumamount of catalyst can also vary with the catalyst chemistry.

[0041] For a preferred catalyst chemistry in the case of:2-ethyl-4-methylimidazoline the range can be from about 1.0% to about8.0% by weight (wt-%) based on the weight of epoxy, chain extender(i.e., amine and/or catechol) and catalyst, and preferably from about 2wt-% to about 7.0 wt-%; 2-benzyl-2-imidazoline the range can be fromabout 3.0 wt-% to about 11.0 wt-% and preferably from about 4.0 wt-% toabout 10.0 wt-%; 4,4′-dimethyl-2-imidazoline the range can be from about3.0 wt-% to about 7.0 wt-% and preferably from about 4.0 wt-% to about6.0 wt-%. Other preferred catalysts can include: imidazole in the rangeof from about 0.25 wt-% to about 3.0 wt-% and preferably from about 0.5wt-% to about 2.25 wt-%; DBUE(1,4-Diazabicycol<5.4.0>undec-7-ene) in therange of from about 4.0 wt-% to about 8.0 wt-% and preferably from about5.0 wt-% to about 7.0 wt-%; 1-butylpyrrolidine in the range of fromabout 3.0 wt-% to about 7.0 wt-%; 1,4,5,6-tetrahydropyrimidine in therange of from about 3.0 wt % to about 8.5 wt %;1,2-dimethyl-1,4,5,6-tetrahydropyrimidine in the range of from about 1.5wt-% to about 6.0 wt-%; and N,N-dimethylbenzylamine in the range of fromabout 4.0 wt-% to about 8.0 wt-%.

[0042] Toughening agents (or elastomeric modifiers) for use in preferredcompositions of the present invention generally comprise: polymericcompounds having both a rubbery phase and a thermoplastic phase such asgraft copolymers having a polymerized diene rubbery core and apolyacrylate or polymethacrylate shell; graft copolymers having arubbery core with a polyacrylate or polymethacrylate shell; andelastomeric particles polymerized in situ in the epoxide fromfree-radical polymerizable monomers and a copolymeric stabilizer;elastomer molecules, separate elastomer precursor molecules; combinationmolecules that include epoxy-resin segments and elastomeric segments;and, mixtures of such separate and combination molecules. Thesematerials are used to improve structural properties including peelstrength. The combination molecules may be prepared by reacting epoxyresin materials with elastomeric segments; the reaction leaving reactivefunctional groups, such as unreacted epoxy groups, on the reactionproduct. The general use of tougheners in epoxy resins is well-known,and is described in the Advances in Chemistry Series No. 208 entitled“Rubbery-Modified Thermoset Resins”, edited by C. K. Riew and J. K.Gillham, American Chemical Society, Washington, 1984, the referencebeing incorporated herein by reference. The amount of toughening agentto be used depends in part upon the final physical characteristics ofthe cured resin desired, and is generally determined empirically.

[0043] Specific examples of useful toughening agents include graftcopolymers having a polymerized diene rubbery backbone or core to whichis grafted a shell of an acrylic acid ester or methacrylic acid ester,monovinyl aromatic hydrocarbon, or a mixture thereof, such as disclosedin U.S. Pat. No. 3,496,250, incorporated herein by reference. Preferablerubbery backbones can comprise polymerized butadiene or a polymerizedmixture of butadiene and styrene. Preferable shells comprisingpolymerized methacrylic acid esters can be lower alkyl (C₁₋₄)substituted methacrylates. Preferable monovinyl aromatic hydrocarbonscan be styrene, alpha-methylstyrene, vinyltoluene, vinylxylene,ethylvinylbenzene, isopropylstyrene, chlorostyrene, dichlorostyrene, andethylchlorostyrene.

[0044] Further examples of useful toughening agents are acrylatecore-shell graft copolymers wherein the core or backbone is apolyacrylate polymer having a glass transition temperature T(g) belowabout 0° C., such as polybutyl acrylate or polyisooctyl acrylate towhich is grafted a polymethacrylate polymer (shell) having a T(g) about25° C. such as polymethylmethacrylate.

[0045] Still further examples of toughening agents useful in theinvention are elastomeric particles that have a T(g) below about 25° C.and have been polymerized in situ in the epoxide before mixing with theother components of the composition. These elastomeric particles arepolymerized from free-radical polymerizable monomers and acopolymerizable polymeric stabilizer that is soluble in the epoxide. Thefree-radical polymerizable monomers are ethylenically unsaturatedmonomers or diisocyanates combined with coreactive difunctional hydrogencompounds such as diols, diamines, and alkanolamines. Examples of theseelastomeric particles are disclosed in U.S. Pat. No. 4,525,181, which isincorporated herein by reference. These particles are commonly referredto as “organosols”.

[0046] Still other toughening agents are rubber modified liquid epoxyresins. An example of such a resin is Kraton™ RP6565 Rubber availablefrom Shell Chemical Company. The modified epoxy resin is made from 85%by weight Epon™ 828 and 15% by weight of a Kraton™ rubber. The Kraton™rubbers are known in the industry as elastomeric block copolymers.

[0047] The toughening agent is preferably used in an amount up to about35 parts by weight per 100 parts of epoxy resin. Above 35 parts oftoughening agent, the composition can become very viscous and mayrequire a preheating or prewarming to facilitate its dispensing. Thetoughening agents of the present invention add toughness to thecomposition after curing. Some toughening agents can react and otherswill not react with the epoxide.

[0048] Other useful toughening agents include: carboxylated and amineterminated acrylonitrile/butadiene vulcanizable elastomer precursorssuch as Hycar® CTBN 1300X8 and ATBN 1300X16 and Hycar® 1072 from B. F.Goodrich Chemical Co.; butadiene polymer such as Hycar® CTB; aminefunctional polyethers such as HCl 101 (i.e., polytetramethylene oxidediamine) a 10,000 MW, primary amine-terminated, compound from MinnesotaMining and Manufacturing Co.; St. Paul, Minn., and Jeffamine® fromHuntsman Chemical Co. in Houston, Tex.; functional acrylic rubbersincluding acrylic core/shell material, such as Acryloid® KM330 and 334from Rohm & Haas; and core/shell polymers, such asmethacrylate-butadiene-styrene (MBS) copolymer wherein the core iscrosslinked styrene/butadiene rubber and the shell is polymethylacrylate(e.g., Acryloid® KM653 and KM680; Rohm and Haas). As used above, foracrylic core/shell materials “core” will be understood to be acrylicpolymer having Tg<0° C. and “shell” will be understood to be an acrylicpolymer having Tg>25° C. Tougheners may include epoxy-terminatedcompounds, which can be incorporated into the polymer backbone. Atypical, preferred, list of tougheners includes: acrylic core/shellpolymers; styrene-butadiene/methacrylate core/shell polymers; polyetherpolymers; carboxylated acrylonitrile/butadienes; and, carboxylatedbutadienes. Advantages can be obtained from the provision of the chainextension agent in a composition with an epoxy resin even in the absenceof a toughening agent as described above. However, particular advantageis achieved from the presence of the toughening agent or combinations ofdifferent agents, as previously suggested. It is a feature of thepresent invention that improved resins as disclosed herein are generallymade particularly susceptible to, or are enhanced with respect to, thebeneficial effects of tougheners.

[0049] When included in the epoxy adhesives of the invention, typicallyin Part A (the catalyst part) the amine or amines used are able toachieve chain extension of the growing polymeric chain during curing.Preferred amines can have a reactive or active hydrogen functionality oftwo. Such useful amines include normally liquid amines compatible inpart A alone or in combination with the catechol used in the adhesive ofthis invention. Useful amines include aliphatic primary monoamines,secondary diamines and other amines having two reactive hydrogens permolecule. Such amines can have other reactive hydrogens if they aresterically or otherwise hindered and are substantially non-reactiveduring curing. Preferred amines are substantially free of electronwithdrawing groups in a position that reduces reactivity of activehydrogens in the amine. Suitable amines can include polyethermonoamines, amido mono- and di-amines, aliphatic primary monoamines,polyether diamines with secondary nitrogen groups, diamines withsecondary nitrogen groups, monoalkanolamine, etc. Preferred aminecompounds can include compounds of the formula:

[0050] wherein R, R₁ and R₂ are independently selected from the groupconsisting of aliphatic, aryl (aromatic) or hydrogen; wherein n and mare numbers independently selected from 0 to 3; x is a number thatranges from 0 to 10; and Y can be —O— or —S—. In another amine, possiblyuseful in limited amounts, Y is —NH—.

[0051] An additional embodiment of the chain extender amines arecompounds according to the formula:

R₁—NH—(CH₂)_(X)—R₃—(CH₂)_(X)—NH—R₂

[0052] wherein R₁ and R₂ are independently selected from the groupconsisting of alkyl, benzyl, —CH₂—CH₂—CN; R₃ is independently selectedfrom the group consisting of —CH₂—, —S—, —O—CH₂—CH₂—O—, or arylenestructures including phenylene or naphthalene and each x isindependently a number that ranges from 1 to 3. In another amine,possibly useful in limited amounts, R₃ is —NH—.

[0053] A third embodiment of the chain extender amine compounds arecompounds of the formula:

[0054] wherein R₂ is an aliphatic group or an aromatic group, containing1 to 18 carbon atoms and R₁ and R₃ are R₂ or H.

[0055] One specific embodiment of the chain extender amine of thepresent invention comprises alkyl amino substituted morpholine (e.g.,4-(3-aminopropyl)morpholine). Another amine, possibly useful in limitedamounts, may be an alkyl amino substituted piperazine. Each of theseamines has the following formula:

[0056] wherein Y is —O— for the alkyl amino substituted morpholine and Yis —NH— for the alkyl amino substituted piperazine.

[0057] It can be desirable for the above amines to be used in theadhesive at amounts in the range of from about 0.5 wt-% to about 20wt-%, preferable from about 2 wt-% to about 15 wt-%, based on all of thereactive components (i.e., the epoxy resin, catalyst and chainextender). When catechol and an amine are used together, it can bedesirable for the catechol/amine weight ratio to be in the range of fromabout 4 to about 0.5 parts of catechol per 1 part by weight of amine,and preferable at least about 1 part catechol per 1 part by weight ofamine.

[0058] It has been found that the risk of the catechol recrystallizingcan be effectively eliminated, or at least significantly reduced, byadding some resorcinol and/or amine as part of the chain extender. Theuse of a liquid amine can help to prevent recrystallization of thecatechol, when the catechol is mixed with the amine, depending on thesolubility of the catechol in the amine. The use of a liquid catalystmay also help to prevent recrystallization of the catechol, when thecatechol is mixed with the catalyst, depending on the solubility of thecatechol in the catalyst. Preferably, the catechol is soluble in boththe catalyst and the amine, when an amine is used. Furthermore, it hasbeen found that the addition of an amine can provide faster reactivity(i.e., shorter curing times) and greater latitude in the mix ratiobetween parts A and B. By adding an amine in the chain extender, theadhesive composition can gel more quickly to a tack free state. Howquickly the composition gels depends on the amount and type of amineused. If the amine concentration is too high, it may impact performanceof the adhesive composition.

[0059] Various adjuvants may be added to compositions according to thepresent invention, to alter the characteristics of the curedcomposition. Included among useful adjuvants are: corrosion inhibitorssuch as some silica gels; thixotropic agents such as fumed silica;pigments such as ferric oxide, brick dust, carbon black, and titaniumoxide; reinforcing agents such as silica, magnesium sulfate, calciumsulfate, and beryllium aluminum silicate; clays such as bentonite; andany suitable filler. Amounts of up to about 50 parts of adjuvant, andpossibly more, per 100 parts of liquid adhesive components may beeffectively utilized. Generally, the toughening agent is pre-dispersedin the epoxide compound. The toughener-containing epoxide part B is thenmixed with a curative part A, with the chain extension agent in the partA, the part B or both parts, to form a substantially uniform mixture.

[0060] The mixture is cured upon heating for an appropriate length oftime. While partial curing reaction may take place slowly at roomtemperature, full cure is preferably brought about by heating themixture to a temperature in the range of from about 130° C. to about200° C. for an appropriate length of time. A typical heating cycle maybe 20 minutes at 163° C. Generally, as the curing temperature increases,the curing time decreases.

[0061] The adhesives of the invention may be used, for example, toassemble panels or other sheet-like structures with frame members. Asshown in FIG. 6, the adhesive may be used in combining a panel with ahydroformed tube frame structure using self-positioning means to holdthe parts in a correct alignment while the adhesive cures. Such anassembly system is a substantial advancement over other systems. Inaddition, the adhesive may be useful in bonding together members of aspace frame. Furthermore, the adhesive may be used, for example, in anautomobile to bond weld paddles onto an intrusion beam in order to makea door intrusion beam assembly. The adhesive may also be used toadhesively bond the door intrusion beam assembly in the automobile door.Welding (e.g., tack welding) or mechanical fastening could be used tofix the adhesively bonded paddles in place until the adhesive cures. Itmay also be desirable to use the adhesive to bond hydroformed tube steeltogether in order to make an automobile space frame assembly. Anotheruse for the adhesives of the invention involves hem bonding of twosubstrates with an appropriate mechanical structure. In hem bonding, anadhesive mass is formed between the edges of two substrates brought intoclose alignment. The edges of the substrates are bent in an overlappingfashion to form a folded or bent edge structure with the adhesive foundbetween the substrates throughout the folded or overlapped edge. Thethus formed edge structure can then be cured through induction heatingor other common heat curing methods (e.g., infrared radiation, forcedair, immerson, etc.).

[0062] In areas of adhesive bonding, the adhesive can be applied as acontinuous bead, in intermediate dots, stripes, diagonals or any othergeometrical form that will conform to forming a useful bond. Suchadhesive placement options can be augmented by welding. The welding canoccur as spot welds, as continuous seam welds, or as any other weldingtechnology that can cooperate with an adhesive mass to form amechanically sound joint that has adequate fatigue and impact resistanceand load bearing performance. Such welding can occur around or throughthe adhesive bonds. The heat of welding can augment other curing energyinputs (e.g., oven baking, induction heating, etc.).

[0063] The specification provides an explanation of the components andprocessing used to make and use the epoxy compositions of the invention.The following examples and data further exemplify the invention anddemonstrate the advance in structural adhesives achieved by thisinvention.

[0064] Preparation of Substrates

[0065] FPL Etched Aluminum Substrate: The aluminum substrate is a 102 mmby 178 mm by 0.8 mm thick sheet of 2024T-3 Alclad aluminum obtained fromAlcan Corporation. Each sheet or coupon is treated as follows beforetesting: 1) soaking for 10 minutes in Oakite™165 caustic wash solution,obtained from Oakite Corp., St. Paul, Minn., at a temperature of 85° C.;2) the sheets (in a rack) are submerged in tank of tap water for 10minutes; 3) spray rinsing with tap water for 2-3 minutes; 4) soaking ina tank of FPL etch (a hot solution of sulfuric acid and sodiumdichromate from Forest Products Laboratory of Madison, Wis.) at 66° C.for 10 minutes; 5) spray rinsing with tap water for 2-3 minutes; 6) dripdrying for 10 minutes at ambient temperature and then for 30 minutes ina re-circulating air oven at 54° C.; 7) spraying a primer (EC3960available from 3M Company, St. Paul, Minn.) to a coating thickness of0.25 to 0.50 mm; 8) drying at ambient temperature (about 23° C.) for 30minutes followed by drying in a re-circulating air oven at about 121° C.for one hour.

[0066] Steel Substrate: The steel substrate is a 25 mm by 100 mm by 0.8mm thick coupon of hot dipped minimum spangled galvanized steel (G60HDMSobtained from National Steel Corporation, Livonia, Mich.) unlessotherwise noted. The steel is cleaned by applying methyl ethyl ketone(MEK) to the surfaces, wiping with cheesecloth, and then drying forabout 10 minutes at room temperature.

[0067] Lubricated Steel Substrate: A lubricated steel substrate isprepared by taking the steel coupon described above that has beencleaned with methyl ethyl ketone and then applying a controlled coatingweight of 61MAL automotive lubricant obtained from Quaker Corp., ChicagoIll., unless otherwise noted. The lubricant is applied with anEppendorf® Repeater™ Pipette #4780 with a 1 microliter tip. A setting of#4 on the pipette dial was used to dispense 3 drops of lubricant (i.e.,12 microliters) onto the cleaned steel surface, and then smeared to aneven coating with a latex gloved finger. The coating weight is measuredto be about 400±50 milligrams per square foot (about 4.3±0.54 g/m²).

Test Methods

[0068] Test Method A: T-Peel Adhesion Test on an FPL Etched AluminumSubstrate

[0069] The aluminum sheet substrate is prepared as described above forFPL Etched Aluminum. The test adhesive is applied over the entire primedsurface. Glass fibers (diameter 0.13 mm) are then laid across theadhesive at a 45 degree angle at a density of about one fiber every 25.4mm. A second prepared aluminum test substrate is placed over the firstone at a 12.7 mm offset in the lengthwise dimension to facilitateopening of the bond for a T-peel configuration and with the preparedsurface against the adhesive. The sample is then placed between two 203mm by 203 mm by 6.4 mm thick steel plates, put into a press applying27.6 kiloPascals (kPa), and cured at about 121° C. for 60 minutes. Thelaminate is then allowed to equilibrate at 23° C. and 50% relativehumidity (RH) for 24 hours. Test samples measuring 25.4 mm by about 178mm test sample are cut from the sheet and tested for T-peel on anInstron Tensile Tester following ASTM D1876-72 at a crosshead speed of127 mm-min⁻¹. Results are reported in Newtons per centimeter (N-cm⁻¹.

[0070] Test Method B: T-Peel Adhesive Strength on Steel or LubricatedSteel Substrate

[0071] The test adhesive is spread over the prepared surface of twosteel or lubricated steel coupons described above except for a 15-20 mmsection left free of adhesive on the opposite ends of each test strip.The adhesive contains solid glass beads having a diameter of 0.25mm±0.01 mm, obtained from Cataphote, Inc., Jackson, Miss. The beads areused to control bondline thickness and the adhesive is spread with aspatula by applying pressure so that the spatula is contacting the glassbeads. The two strips are brought together, and clamped with two mediumsized binder clips along each of the 100 mm edges. The coupons remainclamped together and are placed in a forced air oven at 163° C. for 20minutes to cure the adhesive and form a coupon assembly. Thenon-adhesively bonded ends of the coupon assembly are each then priedopen to form a T-shaped configuration at either end of the couponassembly. The coupon assembly is then allowed to equilibrate at roomtemperature. The T-peel strength is performed according to ASTM Method D1876-72 using an Instron Tensile Tester at a crosshead speed of 127mm-min⁻¹. Results are reported in Newtons per centimeter (N-cm⁻¹).

[0072] Test Method C: Overlap Shear Test for Aluminum Substrate

[0073] Test sheets of aluminum are prepared as described for the T-peeltest. The test adhesive is applied over about 12.2 mm of a primed sheetof aluminum. Glass fibers are applied at a 45 degree angle as describedabove. The primed surface of a second sheet of aluminum is pressed intothe adhesive such that the second sheet overlaps the adhesive 12.7 mmwith the non-adhesive portions of each of the sheets extending inopposite directions. The sample is cured between steel plates asdescribed above, and then conditioned at 23° C. and 50% RH for at least24 hours. Test samples measuring 25.43 mm in width are cut from thecured sample. Overlap shear strength is determined on an Instron TensileTester following ASTM TM D1002-72 at a crosshead speed of 50 mm per min.

[0074] Test Method D: Overlap Shear Strength on Cleaned Steel orLubricated Steel

[0075] The test adhesive is applied over 12.72 mm on one end of two 25mm by 100 mm cleaned steel or lubricated steel coupons and spread downto the level of glass bead particles contained within the adhesive, asdescribed above for Test Method B. The two adhesive coated ends arepressed together forming a 12.72 mm overlap with the non-adhesive endsof the coupons extending in opposite directions. The overlapped couponsare clamped together at the adhesive ends using a 0.94 cm capacitybinder clip (No. 1002 available from IDL MFG and Sales Corp., Carlstadt,N.J.). The clamped assembly is then cured in a forced air oven at 163°C. for 20 minutes. The laminate is then allowed to equilibrate at roomtemperature. Overlap shear strength is determined according to ASTMD1002-72 with an Instron Tensile Tester at a crosshead speed of 50 mmper minute. Test results are reported in megaPascals (MPa).

[0076] Test Method E: Impact Peel Test (Dynamic Wedge Impact)

[0077] This test is used to evaluate the relative ability of an adhesivebonding system to dissipate energy in the peel mode during an impactload. The method is a Ford Laboratory Test Method and is an extension toISO Method 11343 with the same specimen size and wedge shape as the ISOmethod.

[0078] The wedge shape is shown in FIGS. 1 and 2. It measures 117.3 mmin height and 20 mm at the base with a radius of 1.0 mm at the tip foran angle of 8.8°, and is fabricated from hardened steel. The impactportion of the test transducer (hammer) is fabricated from hardenedsteel and measures at least 25 mm by 5 mm in thickness to insure impactover the entire top of the test assembly. In FIG. 1, the test wedgeshaped 10 is shown having a base 11 secured using drilled and tappedmounting napatures 12 and the wedge 13. In FIG. 2, a top view of thewedge showed in side view in FIG. 1 is shown having the wedge 13′, thebase 11′ and the tapped and drilled holes 12′.

[0079] The test is performed using an instrumented impact testingmachine called a Dynatup Impact Test Machine, Model 8250 made by InstronCorp. (formerly General Research Corp.) of Canton, Mass. The impacthammer is a force transducer classified as a drop weight “tup”.

[0080] The test substrates used are MEK (methyl ethyl ketone)cleaned G60hot-dipped minimum spangled galvanized metal coupons (obtained fromNational Steel Corp.) measuring 20 mm×90 mm×0.78 mm with tolerance onlength and width being ±0. 1 mm. Test specimens are prepared by firstaligning two metal coupons so that their 90 mm sides are touching. Then19 mm wide Kapton tape (3M Company tape # 5419) is applied to a distanceof 30±0.2 mm from the ends of both coupons across both coupons. The testadhesive is applied to the 30 mm exposed surface at the ends of bothcoupons, as described above for Test Method B. Any adhesive on theKapton tape surface is removed. Both coupons are pressedtogether—adhesive to adhesive—and excess adhesive that has squeezedbeyond the edges is removed. The test assembly is then clamped withmedium size binder clips followed by curing at 163° C. for 20 minutes.The cured test assembly is then allowed to equilibrate at roomtemperature prior to testing. FIG. 4 shows the appropriate configurationwith the coupons 21 and 22 having the test adhesive mass 23 adhering thecoupons.

[0081] The test assembly and wedge are maintained at a constanttemperature specified for the test (23° C. or 90° C., both ±1° C.). Theassembly is marked 40.0±0.2 mm from the bonded end for consistentplacement on the wedge. The nonbonded end of the assembly is thenslipped over the wedge 10 and pushed down until reaching the 40 mm mark.The assembly is not prebent, but allowed to conform to the shape of thewedge. FIG. 4 shows the appropriate configuration with the coupons 21and 22 with the test adhesive mass 23 adhering the coupons. The assemblyis positioned on the wedge knife edge so that it is square with respectto the wedge and impact hammer and that the hammer hits the entire topof the test assembly simultaneously. The test machine is activated byimpacting the specimen with a falling weight 31 of 44.8 kg at 2meters-sec⁻¹. FIG. 5 shows the specimen of FIG. 4 after the applicationof the force. Test results are reported as Crack Propagation Load inKiloNewtons (kN) and the measured Energy in Joules (J) required to splitapart the assembly. Test temperatures are reported as +23° C. and 90° C.

[0082] Test Method F: Sustained Load Durabilty (SLD)

[0083] This test is used to evaluate the relative durability of anadhesive bond when exposed simultaneously to a tensile load andenvironmental aging. The test substrate is a 25 mm by 76 mm steel coupon(G60HD steel available from National Steel, unless otherwise indicated)that has been lubricated with 61 MAL lubricant at a coating weight of4.3 grams per square meter (400 miligrams/ft²). The sample is preparedas for the overlap shear test. The adhesive, containing 0.25 mm diameterglass beads to control the bond line thickness, is applied to a 1.27 cmlong area on the oiled side of one coupon. A second oiled coupon isplaced over the adhesive and the sample is clamped. The sample measures14 cm in length with an overlap adhesive bond measuring 1.27 cm in themiddle. Excess adhesive that squeezes out of the edges is removed priorto curing. The sample is cured in an oven at 163° C. for 20 minutes. Thesample is then allowed to equilibrate at room temperature beforetesting.

[0084] Each end of the sample is punched with a 6.35 mm hole that iscentered 1.27 cm in from each end. For a single test, five samples arearranged and bolted end to end in alternating fashion so that thebondlines are aligned along the center of the test fixture. Stainlesssteel bolts (6.35 mm dia. by 19.05 mm long) with corresponding nuts andnylon washers having a 19.05 mm diameter were used to bolt the samplestogether to form a string of five samples.

[0085] The test fixture is a stainless steel U-channel measuring 63.5 cmlong by 5.1 cm wide by 2.5 cm high. The walls of the U-channel are 0.3cm thick. The U channel has a spring attached to one end and a fixed endblock attached to the other end. The fixed end block is a 5.7 cm by 4.3cm steel block having a 3 cm by 4.3 cm by 1 cm thick block cut out ofone end to form a step in the block. The stepped end block fits into thechannel with the stepped portion facing the inside length of thechannel. The end block is bolted to one end of the U-channel and a boltaffixed at the center of the stepped portion of the end block is used toattach the test samples. The other end of the U-channel has a fixed endcap with a 24 mm by 1.2 cm diameter threaded rod extending through it.Within the channel, the rod is attached to an end block similar to theone on the opposite end except that this end block is free to move asthe threaded rod is turned. A 304 coiled stainless steel spring havingan I.D. of about 2.5 cm, a length of 9.7 cm, and a spring rate ofapproximately 15 kg-mm⁻¹ (available from Century Spring Corp., LosAngeles, Calif.—part # is RV-43190), with fitted endcaps and washers oneach end of it, is placed over the threaded rod. A hex nut is placedover the threaded rod to hold the spring in place. A hollowed outcylinder having an inside diameter that is slightly larger than theouter spring diameter is placed over the spring to prevent lateraldeflection of the spring. The amount of deflection in the spring equalto 226.8 kilograms was determined by compressing the spring on anInstron 4210 compression tester to that weight and measuring thecompressed length of the spring. The compressed length was approximately85% of its original length.

[0086] For the test, the string of samples is bolted to each of the endblocks inside of the U-channel and the spring is compressed to thecalibrated compression length to yield a tensile stress of 7 MPa. Therack of samples under a tensile stress are aged in the test cycle below.One day represents one cycle (i.e., 24 hours). The test is typicallystarted on a Monday morning, and five cycles are run during the week(i.e., five days a week). The rack is left in the controlled environmentcabinet over the weekend with no immersion in the salt solution. Weekenddays are not counted as cycles. Test results are reported in cycles. Thesteps of each cycle are as follows:

[0087] 1. The rack is first immersed in a salt solution (5% by weightsodium chloride in distilled or deionized water) at 23±2° C. for 15minutes.

[0088] 2. The rack is then removed from salt solution and allowed todrip dry vertically at 23±2° C. for 105 minutes.

[0089] 3. The rack is next placed in a controlled environment cabinet at50±2° C. and 90±5% relative humidity for 22 hours. The rack is checkeddaily for failure. If one of the lap shear samples in a rack fails, thesample is removed and a spacer is bolted in its place to maintain theappropriate stress.

[0090] 4. Cycling is continued until three bonds have failed, noting thecycles to failure for each bond. The number of cycles to failure for thethree bonds is averaged and then recorded.

[0091] Test Method G: Fatigue Test

[0092] This test is a measure of cyclic fatigue resistance as measuredby the total number of cycles that an adhesive bond endures and theamount of crack propagation in the bond. Test samples are prepared asfor Test Method B (T-peel Adhesion) described above except that thecoupons are bent 90 degrees to form a 2.5 cm tab where the bend radiusis half of the metal thickness. The coupons are 0.7 mm thick 70G70GEdraw quality electro-galvanized steel from National Steel. The bentcoupons are degreased as described above in steps 1), 2), 3) and 6) ofthe FPL Etched Aluminum substrate. Coupons are drip-dried for 10 minutesat ambient temperature, then placed in a recirculating air oven at 54°C. for 30 minutes to dry. The dried coupons are placed in a sealedpolyethylene bag and stored in a dessicator until the bonds are made.

[0093] Prior to application of the adhesive, a 2.5 cm wide strip of 5419Kapton Tape available from 3M Company, St. Paul Minn., is applied acrossthe end of the tab on the adhesive side of each coupon so that the tabis essentially covered by the tape. The adhesive is then applied, asdescribed above for Test Method B, to the untaped surface of the tapedside of each coupon up to the edge of the tape. The adhesive coatedsurfaces of two such coupons are brought together and clamped with twomedium sized binder clips along each edge of the coupons. Excessadhesive that squeezes out is removed. The clamped assembly is thenplaced in a forced air oven set at 163° C. for 20 minutes to cure theadhesive. The tape is not removed from the tabs. The test assembly isallowed to equilibrate at room temperature prior to testing.

[0094] The test is conducted on an MTS 880 tensile testing machine setin a constant load mode for a 20 Hertz sinusoidal cycle with +222.4Newtons force for maximum load and 22.2 Newtons for minimum load. Thetabbed (i.e., taped) ends of the bond assembly are inserted into thegrips and the grip edges are positioned equidistant from the center ofthe bondline. The test assembly is preloaded to a 0.055 mm displacementprior to initiating cycling. Automatic termination of the cycling wouldoccur if vertical displacement exceeded 6.35 mm. The adhesive of Example172 exhibited 3,391,000 cycles at which time the test was manuallyterminated with negligible crack propagation (less than 1 mm).

Identification of Components Used in the Examples

[0095] Epon™828 Epoxy Resin—diglycidyl ether of Bisphenol A having anepoxy equivalent weight of about 190 and an average molecular weight of350-400, and available from Shell Chemical Company.

[0096] Epon™ 58006 resin (Toughener)—Epoxy resin adduct having 40% byweight Hycar 1300X8 and 60% by weight Epon 828 available from ShellChemical Company

[0097] Paraloid™BTA IIIF copolymer (Toughener)—methylmethacrylate/butadiene/styrene copolymer available from Rohm & HaasCompany.

[0098] PARALOID™ EXL2600 (Toughener)—Methacrylate/butadiene/styrenecore-shell polymer available from Rohm & Haas.

[0099] MK107 Reactive Diluent—diglycidyl ether of cyclohexane dimethanolavailable from Shell Chemical Company.

[0100] GP-71 silica—silicon dioxide having a particle size in the rangeof from about 20 to about 30 micrometers, available from Harbison-WalkerCorp.

[0101] Cab-0-Sil™TS-720 silica—fumed silica available from Cabot Corp.

[0102] “B37/2000” glass bubbles—glass bubbles available from MinnesotaMining & Manufacturing Company.

[0103] Glass Beads—solid glass beads having a diameter of 0.25 mm±0.01mm, obtained from Cataphote, Inc., Jackson Miss.

[0104] Other chemical compounds used can be obtained from chemicalsupply companies such as Aldrich Chemicals.

EXAMPLES 1-20

[0105] A first epoxy resin premix composition (Premix I) was prepared bymixing 500 grams of Epon™828 epoxy resin with 125 grams ofParaloid™EXL2600 copolymer using a high shear mixer between 110-120° C.for about 30 minutes, and then cooling to ambient temperature. A secondepoxy resin premix composition (Premix II) was prepared by combining 243grams of Epon™828 epoxy resin with 130 grams of catechol in a glass jar,flushing with nitrogen, and heating at 121° C. for 15 minutes withoccasional stirring until a clear homogeneous (i.e., no apparent phaseseparation or recrystallization) solution was formed. The mixture wascooled to ambient temperature. Part B of an epoxy resin composition wasprepared by mixing 335 grams of Premix 1,339 grams of Premix II, 65grams of MK107 reactive diluent, 201 grams of GP-71 silica, 30 grams ofK37 glass bubbles, 17 grams of Cab-0-Sil™TS-720 silica, and 12 grams ofglass beads in a planetary mixer under vacuum for about 20 minutes. Theresulting composition had a smooth paste-like consistency.

[0106] Two-part epoxy adhesive compositions were prepared by mixingvarying amounts of Part A (catalyst only) shown in Table 1 and 5.0 gramsof Part B. The amounts of catalyst are shown as a percent of the totalformulation (%T), by weight in grams (Part A—grams) and also as apercent of the reactive species (%Cat), i.e., the amounts of epoxy,catechol, and amine from the catalyst. The catalyst used for Examples1-7 was 2-ethyl-4-methylimidazoline; the catalyst for Examples 8-14 was2-benzyl-2-imidazoline; the catalyst for Examples 15-20 was4,4-dimethyl-2-imidazoline. The active hydrogen to epoxy molar ratio forthese examples (i.e., OH-Amine/Epoxy ratio) was maintained at about 0.8for each of these examples. In calculating this ratio, any aliphatichydroxyls present in an exemplary amine (e.g., 3-amino-1-propanol) werenot considered. The “OH” referred to in the OH-Amine/Epoxy ratio refersto a phenolic OH (i.e., from the phenolic chain extender), and the“Amine” refers to any NH₂ and/or NH from the amine chain extender andcatalyst.

[0107] The adhesives were tested for Impact Peel Resistance, as measuredby crack propagation load in kiloNewtons (kN) and total energy in Joules(J) at 23° C. and 90° C. according to the test described above. Theadhesives were also tested for T-peel adhesion at 23° C. on the abovedescribed steel substrate. Test results are shown in Table 1. TABLE 1Energy Load Energy Load T-Peel % Part A (J) (kN) (J) (kN) N-cm⁻¹ Ex Tgrams % Cat @ 23° C. @ 23° C. @ 90° C. @ 90° C. @ 23° C. 1 1 0.05 1.47NT NT NT NT 0 2 2 0.10 2.88 2 0.1 27 0.8 2 3 3 0.15 4.27 15 0.4 22 0.7114 4 4 0.20 5.62 17 0.5 27 0.8 128 5 5 0.25 6.93 12 0.4 24 0.7 114 6 60.30 8.20 2 0 17 0.5 2 7 7 0.35 9.44 0 0 0 0.1 0 8 1 0.05 1.47 0 0 NT NT0 9 2 0.10 2.89 0 0 NT NT 0 10 3 0.15 4.27 8 0.3 NT NT 114 11 4 0.205.62 5 0.2 NT NT 88 12 5 0.25 6.93 16 0.5 NT NT 105 13 6 0.30 8.20 150.5 NT NT 105 14 7 0.35 9.44 11 0.3 NT NT 93 15 1 0.05 1.47 0 0 NT NT 016 2 0.10 2.89 2 0.1 NT NT 67 17 3 0.15 4.27 9 0.3 NT NT 102 18 4 0.205.62 12 0.4 NT NT 119 19 5 0.25 6.93 2 0.1 NT NT 44 20 6 0.30 8.20 1 0.1NT NT NT

[0108] data in Table 1 show that an imidazoline catalyst can providesuperior Impact Peel Resistance at 23° C. and 90° C., as well assuperior T-peel adhesion at 23° C., over an optimum concentration rangeof catalyst.

EXAMPLES 21-38

[0109] Part B of an epoxy adhesive composition was prepared as inExamples 1-20. An epoxy adhesive was prepared by mixing 5.0 grams ofPart B with varying amounts and types of tertiary amine and cyclicamidine catalysts as shown in Table 2. The amounts of catalyst are shownin grams and as a weight percent of the total weight of the reactivespecies (epoxy, catechol, and catalyst) and ranged from 1.47% to 9.44%.The OH-Amine/epoxy ratio was maintained at about 0.8. The adhesivecompositions were tested adhesion on steel substrates, as describedabove.

Examples C1-C5

[0110] The adhesives of Examples C1-C5 were prepared in the same manneras Examples 21-38 except that the catalysts used that did not result ina suitable adhesive. The specific compounds and corresponding test dataare shown in Table 2. TABLE 2 Ex Catalyst T-Peel - N-cm⁻¹ at varying %Catalyst Catalyst Concentration - grams .05 0.10 0.15 0.20 0.25 0.300.35 Catalyst Concentration - wt % 1.47 2.88 4.27 5.62 6.93 8.20 9.44 212-Ethyl-4-methylimidazoline NT 2 114 128 114 2 0 222-Benzyl-2-imidazoline 0 0 114 88 105 105 93 234,4-Dimethyl-2-imidazoline 0 67 102 119 44 NT NT 241,4-Diazabicyclo<5.4.0>undec-7-ene 0 0 23 88 110 50 NT 251,5-Diazabicyclo<4.3.0>non-5-ene 0 47 79 88 84 NT NT 261,4-Diazabicyclo<2.2.2>octane 0 0 39 NT NT NT NT 27 1-Acetylimidazole123 117 43 26 NT NT NT 28 2-Ethyl-4-methylimidazole 70 67 70 67 NT NT NT29 1-Benzyl-2-methylimidazole 0 53 58 61 63 NT NT 30 1-Butylimidazole 6556 63 53 NT NT NT 31 1-Butylpyrrolidine 35 65 78 79 78 NT NT 321-(2-Aminoethyl)piperidine 0 44 44 53 NT NT NT 33 1-Vinylimidazole 44 5356 60 61 NT NT 34 1,4,5,6-Tetrahydropyrimidine 0 96 93 82 NT NT NT 351-Allylimidazole 40 61 61 63 65 NT NT 36 4-(4-Methylpiperidino)pyridine44 66 67 67 NT NT NT 37 1,2-Dimethylimidazole 35 63 53 44 NT NT NT 38N,N′-Dimethylbenzylamine 31 43 53 61 60 NT NT C1 Tributylamine 0 0 0 0NT NT NT C2 1-Phenylimidazole 0 0 0 0 NT NT NT C32-Ethyl-4-methylthiazole 0 0 0 0 NT NT NT C4 1-Methylindole 0 0 0 0 NTNT NT C5 2-Phenyl-2-imidazoline 0 0 0 0 0 0 0

[0111] The results in Table 2 show how the T-peel adhesion performanceof the epoxy adhesive ns of the invention can vary by using differentamounts and types of catalysts.

[0112] Examples 21, 24, 31, 34, and 38, at varying concentrations ofcatalyst based on the weight the reactive species (%Cat) shown in Table3, were also tested for Impact Resistance as measured by the crackpropagation load and total energy at 23° C. and 90° C., and OverlapShear Adhesion at 121° C. (Shear—MPa) on the steel substrate. TABLE 3Load Overlap Energy (kN) Energy Load Shear % (J) @ (J) (kN) (MPa) ExCatalyst @ 23° C. 23° C. @ 90° C. @ 90° C. @ 121° C. 21 1.47 0 0 9 0.41.1 21 2.89 6.7 0.2 20 0.7 4.8 21 4.27 13 0.3 22 0.6 2.9 21 5.62 12 0.424 0.8 4.3 21 6.93 11 0.3 20 0.6 6.2 21 8.20 2 0.1 18 0.6 4.8 21 9.44 00 16 0.5 4.7 24 2.88 0 0 14 0 1.1 24 4.27 1 0 NT NT 3.5 24 5.62 11 0.3NT NT 2.9 24 6.93 9 0.3 14 0.4 3.3 24 8.20 4 0.2 14 0.5 3.9 24 9.44 20.1 14 0.5 5.3 31 2.88 8 0.2 10 0.3 2.9 31 4.27 8 0.3 14 0.5 2.2 31 5.629 0.3 14 0.5 2.4 31 6.93 9 0.3 15 0.5 2.0 34 2.88 11 0.3 20 0.6 4.2 344.27 13 0.4 16 0.5 4.8 34 5.62 4 0.1 14 0.4 5.0 34 6.93 2 0 11 0.3 5.634 8.20 2 0.1 13 0.4 6.2 34 2.88 7 0.3 9 0.3 1.8 38 4.27 7 0.3 11 0.32.2 38 5.62 9 0.3 13 0.5 1.9 38 6.93 7 0.3 13 0.4 2.0 38 8.20 8 0.3 140.5 1.6

[0113] Table 3 show the impact peel resistance, at room and elevatedtemperature, and the overlap shear strength, at elevated temperature, ofthe compositions of the invention can vary by using different amountsand types of the catalysts of the present invention.

[0114] The catalysts of Examples 21-38 fall within the broad classes ofcatalysts described as substituted cyclic amidines (Exs. 21-25, 27-30,33-35 and 37), tertiary amines (Exs. 26 and 38). pyrrolidines (Ex. 31),piperidines (Ex. 32), or pyridines (Ex. 36). Some cyclic amidines aremore sensitive to substitution chemistries than others. Somesubstituents can help and other substituents can hurt the catalystperformance of a cyclic amidine. The effectiveness of a cyclic amidinecan be severly impaired by the wrong substitution chemistry. Inaddition, what substituent is on the nitrogen or adjacent to thenitrogen of the cyclic amidine linkage can determine the degree ofcatalytic activity exhibited by the catalyst. It is very difficult topredict the effect of a particular substitution chemistry and is,typically, determined by trial and error experimentation. While cyclicamidines can be particularly sensitive to the electron withdrawingeffect of a substituent, they may also be sensitive to stereo chemicaleffects, such as steric hinderance. Tertiary amines can be particularysensitive to a substituent that exhibits a high degree of sterichinderance; therefore, dimethyl substitution can be preferred. Ingeneral, pyrrolidines, piperidines and pyridines begin as less effectivecatalysts, and could become weaker when substituted.

[0115] The catalysts of Examples C1-C5 either were too stericallyhindered (C1), contained too strong of an electron withdrawing group (C2and C5), or were otherwise ineffective as a catalyst (C3 and C4) becauseof their inherent chemistry. In addition to containing a strong electronwithdrawing group, the catalyst of Example C2 may also be stericallyhindered and/or may not have the proper solubility. Some of the othercatalysts used in the Table 2 examples may also be unacceptable forcertain applications. For example, the adhesive of Example 26 may not besuitable (e.g., strong enough) for some structural bonding applications.In addition, the adhesives of Examples 28-33 and 35-38 may not besuitable (e.g., strong enough) for other structural bondingapplications.

[0116] Another way that a catalyst can be ineffective is if it isinsoluble or not adequately soluble in the Part A and B blend. Acatalyst can also be ineffective or less effective when used to bondsome substrates, but very effective when used to bond other substrates.This difference in effectiveness can be caused, at least in part, by theadhesive curing too quickly and not allowing sufficient time for theadhesive to sufficiently wet to the substrate surface. If it cures tooquickly, the adhesive may not have the time needed to adequately wet outand bond to a particular substrate, thereby reducing the overall bondstrength. Some substrates are less affected by rapid cure times,compared to other substrates. For instance, the etched aluminumsubstrates described above can be less sensitive to cure times than thegalvanized steel substrates described above. In particular, even thoughExamples 46 and 49 use the same catalysts as that found in Examples 38and 36, respectively, the adhesives of Examples 46 and 49 (i.e., bondedto the etched aluminum) exhibit dramatically improved T-peel adhesioncompared to the adhesives of Examples 38 and 36 (i.e., bonded to thegalvanized steel). There is also a significant improvement in the T-peeladhesion exhibited by the adhesive of Example 50 (i.e., bonded to theetched aluminum) compared to that of Example 39 (i.e., bonded to thegalvanized steel), even though they are both imidazole catalyzedadhesives.

EXAMPLES 39-42

[0117] A Part B premix composition was made by adding 191 grams of Epon828, 70 grams of MK107, 307 grams of the earlier Part B premixcomposition described for Examples 1-20, 154 grams of Shell resin 58006and 122 grams of catechol to a glass jar, flushing with N2 then placingin an oven at 121° C. These components were allowed to melt withoccasional agitation to form a homogeneous solution. This was thenallowed to cool to ambient temperature, and 767 grams were transferredto a planetary mixing bowl. To this was added 196 grams of GP7I,16.9grams of TS720, 6.8 grams of K37 and 13.5 grams of glass beads. This wasthen mixed under vacumn for 20 minutes to a smooth, paste likeconsistency. To 5 gram portions of the resulting Part B composition wereadded respective amounts of each catalyst, as specified in Table 4. Theamount of each catalyst is indicated in grams and % by weight of thereactive species. The adhesive compositions were tested for T-peeladhesion on steel substrates, as described above. TABLE 4 Ex CatalystT-Peel - N-cm⁻¹ at varying % Catalyst Catalyst Concentration - grams0.05 0.1 0.15 0.20 0.30 0.40 Catalyst Concentration - wt % 1.51 3.024.51 6.01 7.51 9.01 39 Imidazole 114 79 35 NT NT NT 40 1-Phenylimidazole5 NT 10 NT 26 NT 41 2-Phenylimidazole 93 105 88 NT NT NT 421,2-Dimethyl-1,4,5,6-Tetrahydropyrimidine NT 88 NT 140 NT 18

[0118] The catalyst of Example 42 (i.e.,1,2-dimethyl-1,4,5,6-tetrahydropyrimidine) is manufactured by KoeiChemical Company of Osaka, Japan. As can be seen from the data in Table4, the location of the phenyl substitutent on the imidazole ring canhave a significant effect. In the 1 position, the electron withdrawingpower of the phenyl substitutent is powerful enough to render thecatalyst ineffective, as evidenced by the low T-peel strength (see alsoExample C2). In the 2 position, the electron withdrawing power of thephenyl substituent is much less, as evidenced by the relatively highT-peel strength. The electron withdrawing effect of the phenyl group ismore significant in the 2 position on the imidazoline ring (i.e.,substitution in the 2 position has more of a detrimental affect withimidazoline than with imidizole), as shown by Example C5. The type andlocation of a substituent can have more or less of an affect on theproperties of the adhesive.

EXAMPLES 43-51

[0119] An epoxy resin premix composition was made by mixing 1016 gramsof Epon 828 and 194 grams of Paraloid BTA IIIF core shell copolymer atan 84/16 weight ratio in a moderate shear mixer at 110° C. to 120° C.for about 1 hour. The mixture was substantially free of gel particles.Part B of an epoxy adhesive composition was prepared by placing 1000grams of the premix into ajar with 190 grams of catechol. The jar wasflushed with nitrogen and placed in an oven at 121° C. for about 30minutes, with occasional agitation until the catechol disolves. Themixture was then cooled. Epoxy adhesive compositions were prepared bymixing portions of Part B with various catalysts in amounts over therange of concentrations shown in the Table 5. The amounts of catalystwere varied from 0.5% to 6.4% as shown in Table 5 (CatalystConcentration wt-%). The catalyst concentration is the percent ofcatalyst based on the total weight of the reactive species, i.e., theamounts of epoxy, catechol, and catalyst at an OH/Epoxy ratio of about0.8. The adhesives were tested for T-peel adhesion to FPL etchedaluminum substrates using the test method described above. TABLE 5 ExCatalyst T-Peel Adhesion (N-cm⁻¹) Catalyst Concentration - grams 0.5 1.02.0 3.0 4.0 5.0 6.0 7.0 Catalyst Concentration - wt % 0.48 0.96 1.902.82 3.74 4.63 5.50 6.36 43 2-Ethyl-4-methylimidazole NT 5 165 175 NT 2NT NT 44 2-Ethyl-4-methylimidazoline NT 2 166 179 184 210 5 4 451,4-Diazabicyclo<5.4.0>undec-7-ene NT 2 2 2 2 175 168 7 46N,N′-Dimethylbenzylamine NT NT 172 172 168 173 172 NT 47Dimethylethanolamine NT NT 175 170 11 2 2 NT 48Bis(2-dimethylaminoethyl)ether NT NT 172 158 147 9 11 NT 494-(4-Methylpiperidino)pyridine NT NT 14 151 156 161 NT NT 50 ImidazoleNT 140 158 9 2 NT NT NT 51 4-Dimethylaminopyridine 2 9 131 128 79 81 NTNT

[0120] The data in Table 5 show how the T-peel adhesion to FPL etchedaluminum of epoxy adhesive compositions of the invention can vary byusing different amounts and types of catalysts. TheBis(2-dimethylaminoethyl)ether catalyst is a commercially availablecatalyst manufactured by OSI Specialties Incorporated, of Danbury,Conn., under the name Niax A99. The T-peel adhesion of the Example 48adhesive can be much less when bonded to a galvanized steel substrate,like that described above (i.e., less than half that shown in Table 5for about the same catalyst concentrations).

EXAMPLES 52-58

[0121] An epoxy resin premix composition was prepared by mixing 500grams of Epon™828 epoxy resin with 125 grams of Paraloid™EXL2600copolymer using a high shear mixer at about 110° C. for about 30minutes, and then cooling to ambient temperature. Part B of an epoxyadhesive was prepared by mixing 380 grams of the premix composition, 251grams of Epon™828 epoxy resin, 73 grams of MK107 reactive diluent, 229grams of GP-71 silica, 34 grams of K37 glass bubbles, 20 grams ofCab-0-Sil™TS-720 silica, and 14 grams of glass beads in a planetarymixer under vacuum for about 20 minutes.

[0122] A catalyst composition (Part A) was prepared by adding 60 gramsof catechol and varying amounts of 2-ethyl-4-methylimidazoline as thecatalyst (Catalyst Amt—gms) shown in Table 6 to ajar, flushing withnitrogen, and capping the jar. The resulting catalyst composition washeated in an oven at 125° C. with occasional agitation to form a Part A.The Part A was then cooled to ambient temperature. An epoxy adhesivecomposition was prepared by mixing 5.0 grams of Part B with varyingamounts of Part A shown in Table 6. The specific amount of catalyst ingrams (Catalyst Amt—gms) is shown in Table 6 as well as the specificamount of Part A in grams, and the amount of catalyst as a weightpercent of the reactive species, i.e., epoxy, catechol, amine, andcatalyst (%Cat). The OH-Amine/Epoxy ratio was maintained at about 0.8.The adhesives were tested for Impact Peel Resistance at 23° C. and 90°C. and Overlap Shear Adhesion at 121° C. to the galvanized steelsubstrates, as previously described, and the test results are shown inTable 6. TABLE 6 Energy Load Energy Load Overlap Shear Catalyst Part A(J) (kN) (J) (kN) (MPa) Ex Amt - gms (gms) % Cat. @ 23° C. @ 23° C. @90° C. @ 90° C. @ 121° C. 52* 4.7 0.81 1.46 0 0 NT NT 0.6 53* 9.9 0.842.89 7 NR NT NT 4.5 54 15.2 0.88 4.33 24 0.8 29 0.9 5.6** 55 21.4 0.915.75 24 0.7 32 1.0 6.6** 56 28.1 0.94 7.16 21 0.6 32 1.1 7.0** 57 35.60.97 8.59 7 0.3 28 0.8 5.4** 58 43.9 1.00 10.00 5 0.1 24 0.8 NT

[0123] The data in Table 6 show how Impact Peel Resistance and OverlapShear Adhesion can vary using a mixture of different amounts of apreferred catalyst and a constant amount of catechol. It is undesirablefor the catechol to recrystallize. Table 6 also shows that for a2-ethyl-4-methylimidazoline catalyst, the catechol is less likely torecrystalize at higher concentrations of the catalyst.

EXAMPLES 59-68

[0124] A catalyst composition (Part A) was prepared by adding 60 gramsof catechol, 40 grams of 3-amino-1-propanol and varying amounts ofimidazole in grams (Cat—gms) as shown in Table 7 to ajar and heating inan oven at 121° C. with stirring for about 10 minutes. The Part A wasthen cooled to ambient temperature. Two part epoxy adhesives wereprepared by mixing about 5 grams of Part B as is described in Examples52-58 with varying amounts of Part A in grams (Part A—gms) shown inTable 7. The amounts of catalyst also shown as a percent of the reactivespecies (%Cat), i.e., epoxy, catechol, catalyst. The OH-Amine/Epoxyratio was maintained at about 0.75 for Examples 59-62 and at 0.8 forExamples 63-68.

[0125] The adhesives were tested for Impact Peel Resistance, T-PeelAdhesion at 23° C., and Overlap Shear Adhesion at 121° C. on steel asdescribed above. Test results are shown in Table 7. Comparative ExamplesC6-C8 are state of the art epoxy adhesives that are used commercially inthe automotive industry and test results are shown in Table 7.Comparative Example C6 is a structural one-part epoxy adhesivemanufactured for Chrysler Corporation under the name MSCD 457B byCemedine, U.S.A. Inc. of Oak Creek, Wis., C7 is a structural one-partepoxy adhesive manufactured for Chrysler Corporation under the name MSCD457C by PPG Industries of Adrian, Mich., and C8 is a structural one-partepoxy structural adhesive manufactured for General Motors under the name998-1989 by PPG. TABLE 7 Overlap Shear T-Peel Energy Ex. Cat. Gms Part Agms % Cat. MPa @ 121° C. N-cm⁻¹ @ 23° C. J @ 23° C. 59 4.8 0.63 0.75 NT88 16 60 9.9 0.64 1.49 NT 70 15 61 21.3 0.66 2.98 NT 96 4 62 34.5 0.684.47 NT 91 4 63 2.2 0.66 0.37 3.6 26 1 64 4.5 0.67 0.75 4.3 91 18 65 6.90.67 1.13 3.8 93 17 66 9.3 0.68 1.50 3.6 79 20 67 11.9 0.68 1.88 4.1 10520 68 14.5 0.68 2.25 4.8 102 16 C6 NA NA NA 1.6 32 2 C7 NA NA NA 2.5 352 C8 NA NA NA 8.9 26 4

[0126] The data in Table 7 show that adhesives of the invention can havean amount of imidazole as a catalyst which provide good Impact PeelResistance and that formulations can be made which are superior overstate of the art structural adhesives. Table 7 also shows that theImpact Peel Resistance of the adhesive can be more sensitive to (i.e.,more adversely impacted by) increases in catalyst concentration thanT-peel strength. So, the T-peel strength can be acceptable while theImpact Peel Resistance is not.

EXAMPLES 69-72

[0127] Part A of an epoxy adhesive composition was prepared as inExamples 63-68 except with varying amounts (in grams) of imidazole shownin Table 8. The other components of Part A were 60 grams of catechol and40 grams of 3-amino-1-propanol as described above.

[0128] Part B of an epoxy adhesive composition was prepared as inExamples 52-58. Epoxy adhesives were prepared by mixing about 5 grams ofPart B with each Part A, containing a different amount of imidazole,shown in Table 8. The amounts of imidazole are shown in grams, as apercent of the reactive species (%Cat) and as a percent of the epoxycontaining species (%Cat/Epoxy), i.e., Epon™ 828 and MK107. TheOH-amine/Epoxy ratio was about 0.8. The adhesives were tested for T-PeelAdhesion on steel substrates at 23° C., as described above.

Comparative Example C9

[0129] An epoxy adhesive was prepared as in Example 69-72 except thatthe amount of imidazole was 0.25% of the epoxy materials, (%Cat/Epoxy)or 0.21% of the reactive species (%Cat). The adhesive was tested as inExamples 69-72. TABLE 8 Imidazole Part A % T-Peel Ex grams grams % CatCat/Epoxy N-cm⁻¹ C9 1.3 0.62 0.21 0.25 0 69 1.9 0.62 0.36 0.30 5 70 2.80.62 0.53 0.44 79 71 3.3 0.62 0.62 0.52 74 72 4.8 0.63 0.89 0.75 79

[0130] The data in Table 8 indicates that useful amounts of imidazolewill be above about 0.35% and, preferably, above about 0.5%, based onthe reactive species.

EXAMPLES 73-81

[0131] Two-part adhesives were prepared by mixing about 5 grams of PartB described in Examples 52-58 with varying amounts and compositions ofPart A (Part A—grams) shown in Table 9. The OH-Amine/Epoxy ratio waskept constant at about 0.8. The amounts of catechol (Catechol grams),3-amino-1-propanol (Amine grams) and 2-ethyl-4-methyl imidazoline(Catalyst grams) were varied as shown in Table 9. The amounts ofcatalyst (i.e., 2-ethyl-4-methylimidazoline) as a percent by weight ofthe reactive materials (% Cat) in the formulations is also shown.

[0132] Part A was prepared by mixing the catechol, amine, and catalyst(i.e., 2-ethyl-4-methyl imidazoline) in ajar, flushed with nitrogen, andheating in an oven at 121° C. with occasional agitation for about 10minutes. The Part A was then cooled to ambient temperature before mixingwith Part B.

[0133] The adhesives were tested for T-peel adhesion at 23° C. oncleaned and lubricated (i.e., lubed) steel, as described above. TABLE 9T-peel Adhesion Catechol Amine Catalyst Part A N-cm⁻¹ Ex grams gramsgrams Grams % Cat Cleaned Lubed 73 80 20 22.9 0.79 3.70 137 137 74 80 2033.6 0.82 5.14 137 122 75 80 20 45.4 0.86 6.59 130 131 76 60 40 24.60.74 3.70 131 105 77 60 40 36.0 0.78 5.15 140 136 78 60 40 48.8 0.816.62 145 140 79 40 60 26.3 0.70 3.71 131 105 80 40 60 38.5 0.74 5.17 158114 81 40 60 52.2 0.77 6.64 158 119

[0134] The data in Table 9 show that at a preferred stoichiometric ratioof OH-Amine/Epoxy of about 0.8, the adhesives of the invention canexhibit superior T-peel adhesion on both clean and lubricated steel overthe range of the catechol to amine weight ratio and catalyst percentage.

EXAMPLES 82-93

[0135] These examples were prepared as in Examples 73-81 except that thestoichiometric ratios (OH-Amine-Epoxy ratio) were varied from about 0.5to about 1.0, and the catechol and amine amounts were variedaccordingly. Part A was mixed with about 5 grams of Part B described inExamples 52-58. The amounts and compositions of Part A are shown inTable 10. The catalyst (2-ethyl-4-methylimidazoline) level was adjustedand is shown as a percent of the reactive species (%Cat). The adhesiveswere tested for T-peel adhesion on both cleaned and lubricated (lubed)steel, as described above. TABLE 10 T-peel Adhesion OH-Amine/ CatecholAmine Catalyst Part A N-cm⁻¹ Ex Epoxy ratio grams Grams Grams Grams %Cat Cleaned Lubed 82 0.5 80 20 55.5 0.56 5.27 40 79 83 0.6 80 20 45.40.65 5.22 56 96 84 0.7 80 20 38.5 0.74 5.18 119 119 85 0.8 80 20 33.60.82 5.14 136 123 86 0.9 80 20 29.9 0.92 5.11 49 61 87 1.0 80 20 27.01.0 5.08 0 0 88 0.5 60 40 60.0 0.53 5.27 44 79 89 0.6 60 40 48.8 0.615.22 53 79 90 0.7 60 40 41.5 0.69 5.20 88 114 91 0.8 60 40 36.0 0.785.15 140 137 92 0.9 60 40 32.0 0.86 5.12 157 131 93 1.0 60 40 29.0 0.955.11 0 0

[0136] The data in Table 10 show that the OH-Amine/Epoxy ratio canaffect the T-peel results, independent of the catalyst concentration. Inaddition, at a relatively constant catalyst level, T-peel adhesion canbe affected by the test substrate, the amounts of catechol and amine,and the OH-Amine/Epoxy ratio.

EXAMPLES 94-132

[0137] For each of examples 94-132, a Part A catalyst composition wasprepared by mixing 60 grams of catechol with the types and amounts ofamines (Amine—grams) and the amounts of 2-ethyl-4-methylimidazoline(Catalyst—grams) shown in Table 11 in a jar. The jars were flushed withnitrogen, capped, and then placed in an oven at 121° C. for 10 minuteswith occasional agitation to form a homogeneous mixture. Thecompositions were then cooled. Part A for each of the examples has a 1:1molar ratio of catechol to amine. The amount of Part A shown in Table 11(Part A—grams) was mixed with about 5 grams of Part B described inExamples 52-58. The OH-Amine/Epoxy ratio was maintained at about 0.8 andthe amount of catalyst based on the reactive materials (%Cat) is shown.T-peel adhesion test results on cleaned steel, obtained according to thepreviously described test method, for all of the Examples 94-132 areshown in Table 11.

[0138] The adhesives of Examples C10-C15 were prepared as for Examples94-132 except that either the Part A recrystallized or the amine wasinsoluble in the Part A. As a result, none of these Examples could betested. TABLE 11 Catalyst Part A % T-Peel Ex Amine Amine Grams GramsGrams Cat N-cm⁻¹  94 3-Amino-1-propanol 41.0 34.0 0.77 4.76 140  952-Amino-2-methyl-1-propanol 48.5 34.5 0.81 4.78 105  96 Benzylamine 58.534.8 0.87 4.74 161  97 2-Methylbutylamine 47.4 34.3 0.81 4.77 152  98Isoamylamine 47.4 34.3 0.81 4.77 131  99 2-Amino-1-methoxypropane 48.634.3 0.81 4.75 131 100 2-(2-Aminoethoxy)ethanol 57.2 34.7 0.86 4.75 145101 Sec-Butylamine 40.0 34.0 0.76 4.75 131 102 Octylamine 71.0 35.0 0.944.68 145 103 Tridecylamine 109.0 36.8 1.16 4.65 119 1043-(Hexyloxy)-1-propylamine 91.5 36.0 1.06 4.82 123 105 Hexylamine 55.528.2 0.84 3.96 140 106 3-(di-n- 101.5 36.5 1.12 4.67 137Butylamino)propylamine 107 N,N′- 131.0 37.5 1.29 4.61 137Dibenzylethylenediamine 108 1-Methylbutylamine 47.4 34.3 0.81 4.77 140109 2-Ethylhexylamine 70.5 35.2 0.94 4.71 149 110 Isobutylamine 40.034.0 0.76 4.77 137 111 Ethanolamine 33.2 33.8 0.73 4.80 123 1126-Aminocapronitrile 61 34.8 0.89 4.73 161 113 4-Aminobenzylamine 66.635.1 0.92 4.73 128 114 Cyclohexylamine 54.5 34.5 0.85 4.72 126 115Oleylamine 151.5 38.3 1.4 4.52 128 116 Decylamine 86.5 36.0 1.0 4.69 131117 Dodecylamine 101.5 36.5 1.12 4.66 137 118 3-(1-Methylethoxy)-1- 67.635.0 0.92 4.71 163 propylamine 119 3-(Isodecyloxy)-1- 123.0 37.3 1.244.63 123 propylamine 120 4-(3-Aminopropyl)morpholine 78.5 35.0 0.99 4.65145 121 4-Amino-1-butanol 48.6 34.4 0.82 4.77 88 1221,8-Diamino-p-menthane 47.0 34.3 0.80 4.74 82 124 Aminomethylbutyne 46.334.3 0.80 4.77 79 125 Tris(hydroxymethyl)amino 66.5 35.0 0.92 4.72 70Methane 126 H221 (Dixie Chemical) 56.7 34.5 0.86 4.72 67 127 2-(2- 38.134.0 0.75 4.77 60 Aminoethylamino)ethanol 128 n-Butylamine 40.0 34.00.76 4.77 61 129 Aminodiphenyhnethane 100.0 36.4 1.11 4.67 44 1301,10-Diaminododecane 47.0 25.8 0.78 3.71 44 131 Diethylenetriamine 22.933.4 0.67 4.78 35 132 3,3′-Diaminodipropylamine 28.4 33.5 0.70 4.79 26C10 Octadecylamine 147.0 38.0 1.38 4.57 R C11 6-Aminocaproic acid 71.535.2 0.95 4.71 I C12 4-Aminobutyric acid 56.2 34.7 0.86 4.75 I C1312-Aminodecanoic acid 117.5 37.0 1.21 4.63 R C14 t-Octylamine 71.0 35.30.94 4.71 R C15 Piperazine 46.9 25.8 0.78 4.66 I

[0139] The data in Table 11 show that the choice of amine chain extendercan impact the performance (e.g., T-Peel Adhesion) of the resultingadhesive. Table 11 also shows that amines, which are useful as chainextenders in the practice of the invention, can include mono-primaryamines and secondary diamines that are not too sterically hindered onthe carbon alpha to the amine or on the amine itself and do not havestrong electron withdrawing groups on amine sites.

EXAMPLES 133-139

[0140] An epoxy resin premix composition was prepared by mixing 500grams of Epon™828 epoxy resin with 125 grams of Paraloid EXL2600copolymer using a high shear mixer at a temperature between 110° C. to120° C. for about 30 minutes and then cooling to ambient temperature.Part B was formed by mixing 330 grams of the epoxy premix, 164 grams ofEPON™58006 resin, 209 grams of Epon™828 epoxy resin, 76 grams of MK107reactive diluent, 231 grams of GP-71 silica, 8 grams of K37 glassbubbles, 20 grams of Cab-0-Sil™TS-720 silica, and 15 grams of glassbeads in a planetary mixer under vacuum for 20 minutes.

[0141] A Part A catalyst composition was prepared by mixing in jars 60grams of catechol with the types and amounts of amines and2-ethyl-4-methylimidazoline catalyst (grams) shown in Table 12. Thenumber of reactive equivalents of amine was maintained relativelyconstant for all of the Examples 133-139 at 0.22. The jars were flushedwith nitrogen then placed in an oven at 121° C. for 10 minutes withoccasional agitation. The compositions were cooled to ambienttemperature. The amount of Part A shown in Table 12 (Part A—grams) wasmixed with 5.0 grams of the Part B described above. The OH-Amine/Epoxyratio was maintained at about 0.8 and the amount of catalyst (%Cat.) isshown based on the weight of the reactive species. The results of T-peeladhesion tests at 23° C. on steel, as described above, are also shown inTable 12. TABLE 12 Amine Catalyst Part A % T-Peel Ex. Amine grams gramsgrams Cat N-cm⁻¹ 133 3-Methoxypropylamine 10.0 26.8 0.84 5.91 149 1342-Amino-1-methoxypropane 10.0 26.8 0.84 5.91 140 1352-(2-Aminoethoxy)ethanol 11.5 26.8 0.86 5.91 152 1363-(2-Methoxyethoxy)propylamine 14.5 27.0 0.89 5.91 152 1373-Isopropoxypropyl amine 13.7 27.0 0.88 5.91 163 138 3-Isohexoxypropylamine 18.5 27.2 0.92 5.88 158 139 3-Isodecoxypropyl amine 25.0 27.5 0.985.85 158

[0142] The data in Table 12 show how the inventive adhesive can beformulated so as to maintain OH-Amine/Epoxy ratio of about 0.8, whilethe molecular weight of the amine is increased, at a constant catalystlevel. The data also show the utility of using ether amines withcatechol as the chain extender.

EXAMPLES 140-153

[0143] A Part A catalyst composition was prepared by mixing in jars 80grams of catechol and 20 grams of various amines with varying amounts of2-ethyl-4-methylimidazoline catalyst (Cat—gms) shown in Table 13. Thejars were flushed with nitrogen, placed in an oven a 121° C. for 10minutes with occasional agitation to form a homogeneous mixture, andthen cooled to ambient temperature. The amount of Part A in grams shownin Table 13 (Part A—gms) was mixed with 5.0 grams of the Part Bdescribed in Examples 133-139. The OH-Amine/Epoxy ratio was maintainedat about 0.8 and the amount of catalyst (% Cat.) is shown based onweight of the reactive species. T-peel adhesion and Impact PeelResistance test results measured as Load in kiloNewtons and Energy inJoules are shown in Table 3. All tests were performed on cleaned steelat 23° C., as described above. TABLE 13 Part A % T-Peel Load Energy ExAmine Cat gms gms Cat N-cm⁻¹ kN J 140 3-Methoxypropylamine 39.0 0.835.95 149 0.6 18 141 2-Amino-1-methoxypropane 39.0 0.83 5.95 145 0.5 16142 2-Amino-1-butanol 39.0 0.83 5.95 140 0.5 15 143 2-Amino-2-methyl-1-propanol 39.0 0.83 5.95 126 0.4 14 144 3- Amino-1-propanol 41.0 0.806.02 145 0.6 18 145 N,N′-Cyanoethylethylenediamine 35.5 0.90 5.95 1310.6 18 146 sec-Butylamine 41.0 0.80 6.00 135 0.5 15 1472-Amino-1-methoxypropane 39.0 0.84 6.00 131 NT NT 1483-Ethoxypropylamine 38.0 0.86 6.01 137 NT NT 149 3-Isopropoxypropylamine37.0 0.88 5.99 119 NT NT 150 2-Ethoxycthylamine 39.0 0.83 5.99 140 NT NT151 2-(2-Aminoethoxy)ethanol 38.0 0.86 6.03 128 NT NT 1521-Amino-2-propanol 40.5 0.81 6.03 131 NT NT 1533-(2-Methoxyethoxy)-propylamine 36.5 0.89 6.01 128 NT NT

[0144] The data in Table 13 show additional useful amines in thepractice of the invention. Examples 145 and 149 are amines manufacturedby Tomah Products Inc. of Tomah, Wis. under the product designationsTomah 159-6 and Tomah PA-7, respectively.

EXAMPLES 154-167

[0145] The exemplary epoxy adhesives were prepared by mixing 0.2 gramsof 2-ethyl-4-methylimidazoline with about 5 grams of the Part B ofExamples 52-58 plus the phenolic compounds of Table 14 in the amountsindicated. An OH-Amine/Epoxy ratio of about 0.7 was maintained. Thecompositions were tested for T-Peel adhesion on steel at 23° C. andresults are shown in Table 13. Comparative Examples C16-C21 wereprepared as for Examples 154-167 except using the phenolic compoundsshown in Table 14. TABLE 14 Amount - T-Peel - Ex Phenolic Grams N-cm⁻¹154 Catechol 0.68 136 155 3-Fluorocatechol 0.8 93 156 3-Methylcatechol0.78 117 157 4-Methylcatechol 0.78 88 158 Resorcinol 0.69 53 1593-Methoxycatechol 0.88 117 160 1/1 equivalents catechol/resorcinol0.34/0.34 137 161 1/1 equivalents catechol/Bisphenol A 0.34/0.71 137 1621/1.8 equivalents catechol/Bisphenol A 0.23/0.91 131 1632,3-Dihydroxynaphthalene 1.0 79 164 None 0 26 165 3,5-Di-t-butylcatechol1.39 46 166 Pyrogallic acid 0.52 35 167 Octylpyrogallol 0.99 26 C162,3-Dihydroxybenzoic acid 0.64 * C17 3,4-Dihydroxybenzoic acid 0.64 *C18 3,4-Dihydroxybenzaldehyde 0.86 * C19 4-Nitrocatechol 0.98 * C20Gallic acid 0.54 0 C21 Lauryl gallate 1.41 0

[0146] the data in Table 14 show the affect of various phenolic chainextenders, including the use of no chain extender, on T-peel adhesionperformance.

EXAMPLES 168-194

[0147] Part B compositions for these two-part epoxy adhesives wereprepared as follows:

[0148] Composition I

[0149] Composition I was prepared by mixing 620 grams of Epon™828 epoxyresin, 82 grams of MK 107 reactive diluent, 251 grams of GP-71 silica, 9grams of K37 glass bubbles, 22 grams of Cab-0-Sil™TS-720 silica, and 16grams of glass beads in a planetary mixer for 20 minutes. The epoxideequivalent weight was 259.

[0150] Composition I

[0151] An epoxy resin premix composition was prepared by mixing 144grams of a polytetramethylene oxide diamine (Toughener A), such as thatdisclosed in U.S. Pat. No. 3,436,359, issued Apr. 1,1969 andincorporated herein by reference, in 5 gram increments over a period of10 minutes to 626 grams of Epon™828 epoxy resin using a Meyers typemixing blade in a quart can at 100° C. Composition II was prepared bymixing 700 grams of the premix with 76 grams of MK 107 reactive diluent,231 grams of GP-71 silica, 8 grams of K37 glass bubbles, 20 grams ofCab-0-Sil™TS-720 silica, and 15 grams of glass beads in a planetarymixer for 20 minutes under vacuum. The epoxide equivalent weight was295.

[0152] Composition III

[0153] Composition III was prepared by mixing 327 grams of EPON™ 58006resin (Toughener B), 372 grams of Epon™828 epoxy resin, 76 grams of MK107 reactive diluent, 231 grams of GP-71 silica, 8 grams of K37 glassbubbles, 20 grams of Cab-0-Sil™TS-720 silica, and 15 grams of glassbeads in a planetary mixer under vacuum for about 20 minutes. Theepoxide equivalent weight was 302.

[0154] Composition IV

[0155] An epoxy resin premix composition was prepared by mixing 140grams of Paraloid EXL2600 copolymer (Toughener C) and 560 grams ofEpon™828 epoxy resin as described above for Examples 52-58. CompositionIV was prepared by mixing 655 grams of the premix composition, 45 gramsof Epon™828 epoxy resin, and 75 grams of MK 107 reactive diluent, 231grams of GP-71 silica, 8 grams of K37 glass bubbles, 20 grams ofCab-0-Sil™TS-720 silica, and 15 grams of glass beads in a planetarymixer under vacuum for about 20 minutes. The epoxide equivalent weightwas 295.

[0156] A premix for a Part A catalyst composition was prepared bycombining 228 grams of 2-ethyl-4-methylimidazoline, 5 grams of a polytetramethylene oxide diamine, and 625 grams catechol in ajar, flushedwith nitrogen, and then capped. 818 grams of the resulting premixcomposition was heated in an oven at 121° C. with occasional vigorousagitation over a period of 30 minutes to form a homogenous solution.After cooling to ambient temperature, the premix was transferred to aplanetary mixer bowl and 12 grams of carbon black (available fromDeGussa Pigments Division of Teterboro, N.J., under the product namePrintex 3), 14 grams of GP7I silica, 21 grams of TS720 silica and 4grams of K37 glass bubbles were added. The Part A composition was mixedunder vacuum for 20 minutes. Because the amount of catechol is aboutthree times the amount of catalyst, there may be a risk of this Part Acomposition recrystallizing. To avoid this risk and still maintain ahigh content of catechol, the amount of catechol in the Part A can bereduced and catechol added to the Part B.

[0157] Epoxy adhesive compositions for Examples 168-194 were prepared bymixing 1.0 gram of Part A with varying amounts of Part B Compositions ingrams shown in Table 15. The Part B was prepared by mixing the amountsby weight of the above Compositions I-IV, e.g., Example 168 has 4.5grams of Composition II and 0 grams of Composition I. The amounts ofPart B were adjusted to maintain an OH-Amine/Epoxy ratio of about 0.8,and the % by weight of each toughener (A, B, C) based on the weight oftotal epoxy is also shown. At increasing concentrations of toughener A,the Part B may thicken with time. Therefore, it may be desirable for theEpoxy composition to be mixed and applied to the substrates soon afterthe Part B is formed. The adhesives were tested for T-peel adhesion at23° C. and Impact Peel Resistance Energy at 90° C. on steel substrates,as described above. The test results are shown in Table 15.

EXAMPLES 169A, 170A, 172A-174A, 177A-182A

[0158] Part B compositions these examples were prepared in the samemanner as for Examples 169-182 except the relative amounts of part Bcompositions I-IV used in Examples 169-182 were adjusted to reflect anOH/epoxy stoichiometry of 0.75. The same part A composition used forexamples 169-182 was used.

[0159] Epoxy adhesive compositions were prepared by mixing 1.0 grams ofthe part A with respective amounts of the part B compositions I-IV shownin Table 15. The adhesives were tested for Impact Peel Resistance at−40° C., −30° C. and −20° C. on steel substrates as described above.Test results are shown in Table 15. TABLE 15 Part B Composition Energy(J) Grams % Toughener T-peel @ Ex I II III IV A B C N-cm⁻¹ 90° C. −20°C. −30° C. −40° C. 168 0 4.50 0 0 20.3 0 0 79 14 — — — 169 1.08 3.26 0 015.2 0 0 82 14 — — — 169A 1.16 3.48 0 0 15.2 0 0 — — 6 4 3 170 2.11 2.110 0 10.2 0 0 70 10 — — — 170A 2.25 2.25 0 0 10.2 0 0 — — 6 4 3 171 0 04.61 0 0 20.3 0 117 17 — — — 172 1.10 0 3.32 0 0 15.2 0 114 17 — — —172A 1.18 0 3.54 0 0 15.2 0 — — 7 7 4 173 2.12 0 2.12 0 0 10.2 0 114 17— — — 173A 2.27 0 2.27 0 0 10.2 0 — — 8 5 3 174 0 0 0 4.50 0 0 20.3 15818 — — — 174A 0 0 0 4.8 0 0 20.3 — — 11 4 3 175 1.09 0 0 3.26 0 0 15.2128 15 — — — 176 2.11 0 0 2.11 0 0 10.2 114 15 — — — 177 0 3.62 0.90 016.2 4.1 0 105 18 — — — 177A 0 3.86 .96 0 16.2 4.1 0 — — 9 8 6 178 02.72 1.82 0 12.2 8.1 0 110 16 — — — 178A 0 2.90 1.94 0 12.2 8.1 0 — —10. 9 7 179 1.72 1.29 1.29 0 6.1 6.1 0 114 20 — — — 179A 1.83 1.37 1.370 6.1 6.1 0 — — 8 7 6 180 0 2.27 2.27 0 10.2 10.2 0 114 20 — — — 180A 02.43 2.43 0 10.2 10.2 0 — — 11 9 6 181 0 1.82 2.74 0 8.1 12.2 0 114 20 —— — 181A 0 1.95 2.92 0 8.1 12.2 0 — — 9 8 6 182 0 0.92 3.66 0 4.1 16.2 0123 NT — — — 182A 0 .98 3.91 0 4.1 16.2 0 — — 8 NT 6 183 0 3.60 0 0.9016.2 0 4.1 96 NT — — — 184 0 2.70 0 1.80 12.2 0 8.1 105 15 — — — 1851.70 1.28 0 1.28 6.1 0 6.1 114 14 — — — 186 0 2.25 0 2.25 10.2 0 10.2119 17 — — — 187 0 1.80 0 2.70 8.1 0 12.2 117 18 — — — 188 0 0.90 0 3.604.1 0 16.2 131 16 — — — 189 0 0 3.66 0.92 0 16.2 4.1 131 18 — — — 190 00 2.74 1.82 0 12.2 8.1 140 20 — — — 191 1.72 0 1.29 1.29 0 6.1 6.1 12819 — — — 192 0 0 2.28 2.28 0 10.2 10.2 152 18 — — — 193 0 0 1.82 2.72 08.1 12.2 140 18 — — — 194 0 0 0.90 3.62 0 4.1 16.2 140 18 — — —

[0160] The data in Table 15 show how varying amounts, types andcombinations of tougheners, with the same Part A composition, can affectT-Peel Adhesion and Impact Peel Resistance.

EXAMPLES 195-199

[0161] Part B compositions were prepared as follows:

[0162] Composition V

[0163] An epoxy resin premix composition was prepared by mixing 436grams of Epon 828 epoxy resin with 68 grams of EXL2600 copolymer using ahigh shear mixer at a temperature between 110° C. to 120° C. for about30 minutes at which time cooling was initiated while mixing continued.When the temperature reached 100° C., 100 grams of catechol was addedwith continued mixing. After 5 minutes a homogeneous mix was obtainedwith no evidence of gel particles or undissolved catechol. Composition Vwas prepared by transferring 550 grams of this premix to a planetarymixer bowl along with 65 grams of MK107 reactive diluent, 155 grams ofEpon 58006 epoxy resin, 199 grams of GP7I silica, 17 grams of TS-720fumed silica, 2 grams of K37 glass bubbles, and 13 grams of glass beadsand mixing under vacuum for 20 minutes to a smooth paste likeconsistency.

[0164] Composition VI

[0165] An epoxy resin premix composition was prepared by mixing 470grams of Epon 828 epoxy resin with 46 grams of Paraloid EXL2600copolymer using a high shear mixer at a temperature between 110° C. to120° C. for about 30 minutes at which time cooling was initiated whilemixing continued. When the temperature reached 100° C., 46 grams ofToughener A (polytetramethylene oxide diamine) were added inapproximately 5 gram amounts over a period of about 10 minutes withcontinuous mixing to obtain a homogeneous solution with no evidence ofundissolved Toughener A. Then 100 grams of catechol were added withcontinuous mixing for another 5 minutes or until a homogenous solutionwas obtained. Composition VI was prepared by transferring 601 grams ofthis premix into a planetary mixer bowl along with 65 grams of MK107reactive diluent, 103 grams of Epon 58006 epoxy resin, 199 grams of GP7Isilica, 17 grams of TS720 fumed silica, 2 grams of K37 glass bubbles,and 13 grams of glass beads and mixing under vacuum for 20 minutes to asmooth paste like consistency.

[0166] Composition VII

[0167] An epoxy/core shell premix was prepared by mixing 560 grams ofEpon 828 epoxy resin with 140 grams of EXL 2600 copolymer using a highshear mixer at a temperature between 110° C. to 120° C. for about 30minutes. 676 grams of this premix was then transferred to a planetarymixing bowl. To this was added 171 grams of 58006, 71 grams of MK107,219 grams of GP7I, 19 grams of TS720 and 14 grams of glass beads thenmixing under vacuum for 20 minutes to a smooth paste like consistency.

[0168] Composition VIII

[0169] An epoxy resin premix composition was prepared by mixing 518grams of Epon 828 epoxy resin with 50 grams of Paraloid EXL2600copolymer using a high shear mixer at a temperature between 110° C. to120° C. for about 30 minutes at which time cooling was initiated whilemixing continued. When the temperature reached 100° C., 50 grams ofToughener A was added in approximately 5 gram amounts over a period ofabout 10 minutes with continuous mixing until achieving a homogeneoussolution showing no evidence of undissolved Toughener A. CompositionVIII was prepared by transferring 562 grams of this premix to aplanetary mixer bowl along with 71 grams of MK107 reactive diluent, 114grams of Epon 58006 resin, 219 grams of GP7I silica, 19 grams ofCab-O-Sil TS720 fumed silica, and 14 grams of glass beads and mixingunder vacuum for 20 minutes to a smooth paste like consistency.

[0170] Composition IX

[0171] A Part B composition was made by combining 197 grams of Epon 828,72 grams of MK107, 317 grams of the epoxy/core-shell premix describedfor Composition VII, 159 grams of Epon 58006 resin, 222 grams of GP7I,19 grams of TS720 and 14 grams of glass beads. This combination wasmixed under vacuum for 20 minutes to a smooth paste like consistency.

[0172] Part A compositions were prepared as follows:

[0173] Composition AA

[0174] A premix composition was made by combining 509 grams of2-ethyl-4-methylimidazoline and 254 grams of catechol in a glass jar,flushing with N2 then heating at 121° C. with occasional agitation toform a homogeneous solution. Composition AA (Part A) was prepared bytransferring 695 grams of the premix to a planetary mixer bowl alongwith 265 grams of GP7I silica, 51 grams of Cab-O-Sil TS720 fumed, and 10grams of K37 glass bubbles. These components were mixed for 5 minutes,then 10 grams of Printex 3 carbon black were added and the entirecomposition mixed under vacuum for 20 minutes.

[0175] Composition BB

[0176] A premix composition was made by combining 250 grams of2-ethyl-4-methylimidazoline, 132 grams of 3-ethoxyproplyamine, 391 gramsof catechol, and 108 grams of resorcinol in a glass jar, flushing withnitrogen, and then heating at 121° C. with occasional agitation to forma homogeneous solution. The resorcinol is added to insure that thecatechol will not recrystallize in the Part A. Composition BB (Part A)was prepared by transferring 800 grams of the premix to a planetarymixing bowl along with 156 grams of GP7I silica, 22 grams of Cab-O-SilTS720 fumed silica, and 18 grams of K37 glass bubbles and mixed for 5minutes. Then 4.5 grams of Printex 3 carbon black were added and mixedunder vacuum for 20 minutes.

[0177] Composition CC

[0178] A premix composition was prepared by combining 238 grams of2-ethyl-4-methylimidazoline, 143 grams of 3-amino-1-propanol, 376 gramsof catechol and 43 grams of resorcinol in a glass jar, flushing with N2then heating a@ 121C with occasional agitation to form a homogeneoussolution. The resorcinol is added to at least help insure that thecatechol will not recrystallize in the Part A. Composition CC (Part A)was then prepared by transferring 727 grams of the above premix into aplanetary mixing bowl along with 208 grams of GP7I silica, 13 grams ofCab-O-Sil TS720, 48 grams of K37 glass bubbles, and 4 grams of Printex 3carbon black. This combination was then mixed for 20 minutes undervacumn. The resulting catechol/3-aminopropanol weight ratio is 70/30.

[0179] Two-part adhesive compositions were prepared by mixing variouscombinations and amounts of the above Part B compositions (CompositionsV, VI, VII, VIII and IX) with the above Part A compositions(Compositions AA, BB and CC) as shown in Table 16. The amounts are givenin grams by weight, and the volumetric mix ratio of Part B to Part A(Mix Ratio—B/A). The adhesives were tested for T-Peel Adhesion andImpact Peel Resistance at 23° C. on steel, as described above. Otherdimensions of the test samples remained as described above. The catalystlevel was maintained at 4% (by weight of the total two-part adhesivecomposition). The effect of the high amine equivalent weight ofToughener A material on stoichiometry is insignificant and is notincluded in the calculations. The OH-Amine/Epoxy ratio was kept constantat about 0.8 respectively. Test results are shown in Table 16. TABLE 16T-Peel Energy Part A Part B Mix Ratio (N-cm⁻¹) (J) Ex Grams Grams B/A @23° C. @ 23° C. 195 1.08 - AA 11.61 - V 10:1  161 NT 196 1.08 - AA11.61 - VI 10:1  140 17 197 2.25 - BB 10.53 - VII 4:1 172 NT 198 2.25 -BB 10.53 - VIII 4:1 145 19 199 2.00 - CC  9.02 - IX 4:1 140 NT

EXAMPLES 200-231

[0180] A Part B composition was prepared as for Examples 52-58. Eachcatalyst composition (Part A) was prepared by adding 47 grams ofcatechol, 47 grams of dodecylamine, and varying amounts of imidazole or2-ethyl-4-methylimidazoline or combinations thereof as the catalyst(Cat—grams) shown in Table 17 to a jar, flushing with nitrogen, and thencapping the jar. The jars of compositions were then heated in an oven at121° C. with occasional agitation to form a Part A. The Part A was thencooled to ambient temperature.

[0181] An epoxy adhesive composition was prepared by mixing 5.0 grams ofPart B with varying amounts of Part A shown in Table 17. The specificamount of catalyst in grams (Cat gms) is shown as well as the specificamount of Part A (Part A gms), the amount of catalyst as a percent ofreactive species, i.e. epoxy, catechol, amine, and catalyst (%Cat) andthe amount of catalyst as a percent of the total adhesive formulation(%T). The OH-Anime/Epoxy ratio was 0.75 for Examples 200-215 and 0.95for Examples 216-231. The adhesive compositions were tested for T-PeelAdhesion and Overlap Sear strength at 23° C. on lubricated steel usingG60HDES galvanized steel and a Fuchs 4107S lubricant at a coating weightof 300 mg-ft⁻². TABLE 17 Imidazole 2-Ethyl-4-methylimidazoline Cat PartA % Cat Part A Shear T-Peel Ex % Cat % T gms Gms Cat % T gms gms MPaN-cm⁻¹ 200 0.075 0.05 0.32 0.88 0 0 0 0 2.5 2 201 0.148 0.10 0.63 0.88 00 0 0 3.3 2 202 0.223 0.15 0.95 0.88 0 0 0 0 3.2 2 203 0.303 0.20 1.300.88 0 0 0 0 8.1 9 204 0.732 0.50 3.20 0.88 0 0 0 0 19.4 102 205 0 0 0 01.49 1.0 6.60 0.90 18.9 67 206 0 0 0 0 2.96 2.0 13.80 0.92 20.1 105 2070 0 0 0 4.44 3.0 21.80 0.95 20.2 131 208 0 0 0 0 5.91 4.0 30.70 0.9719.4 140 209 0.043 0.022 0.15 0.92 2.96 2.0 13.80 0.92 20.1 123 2100.084 0.042 0.29 0.92 2.95 2.0 13.80 0.92 19.5 123 211 0.171 0.085 0.590.92 2.94 2.0 13.80 0.92 20.0 140 212 0.338 0.228 1.60 0.92 2.92 2.013.80 0.92 19.9 131 213 0.020 0.020 0.16 0.97 5.90 4.0 30.70 0.97 20.1140 214 0.041 0.040 0.31 0.97 5.88 4.0 30.70 0.97 20.0 123 215 0.0820.080 0.62 0.97 5.88 4.0 30.70 0.97 19.9 123 216 0.073 0.05 0.26 1.11 00 0 0 3.3 2 217 0.146 0.10 0.52 1.11 0 0 0 0 5.1 2 218 0.219 0.15 0.781.11 0 0 0 0 18.1 88 219 0.294 0.20 1.05 1.11 0 0 0 0 18.3 88 220 0.7430.50 2.70 1.11 0 0 0 0 19.6 114 221 0 0 0 0 1.47 1.0 5.40 1.14 18.8 96222 0 0 0 0 2.92 2.0 11.20 1.16 20.1 131 223 0 0 0 0 4.37 3.0 17.50 1.1819.9 110 224 0 0 0 0 5.80 4.0 24.30 1.21 11.3 9 225 0.043 0.021 0.111.16 2.92 2.0 11.20 1.16 19.9 78.8 226 0.087 0.041 0.23 1.16 2.92 2.011.20 1.16 19.9 70.1 227 0.174 0.082 0.46 1.16 2.92 2.0 11.20 1.16 20131 228 0.347 0.238 1.35 1.16 2.92 2.0 11.30 1.16 19.9 93 229 0.0210.022 0.13 1.21 5.79 4.0 24.30 1.21 NT 2 230 0.041 0.044 0.25 1.21 5.814.0 24.40 1.21 NT 2 231 0.082 0.087 0.50 1.21 5.81 4.0 24.50 1.21 NT 2

[0182] The data in Table 17 show various combinations of imidazole and2-ethyl-4-methylimidazoline as well as individual catalysts alone for astoichiometry (i.e., OH-Amine/Epoxy ratio) of 0.75 and 0.95. The data inTable 17 indicates that when a combination of catalysts are used, lowerconcentrations of each catalyst can be used to provide excellent OverlapShear strength and T-Peel adhesion. In addition, by using a combinationof catalysts at an appropriate level, the performance of the adhesivecomposition (e.g., Overlap Shear strength and T-Peel adhesion) can bemaintained over a broad stoichiometric range, thereby reducing theoff-ratio sensitivity of the composition. For example, compare thedifference between Examples 208 and 224 with the similarity betweenExamples 211 and 227. Furthermore, Table 17 indicates that as theOH-Amine/Epoxy ratio increases, the amount of2-ethyl-4-methylimidazoline in the Part A can have more of an affect onthe T-peel adhesion and Overlap Shear strength (i.e., the T-peeladhesion and Overlap Shear strength become more sensitive to the2-ethyl-4-methylimidazoline concentration at higher stoichiometricratios).

EXAMPLES 232-247

[0183] Part A catalyst compositions were prepared as in Examples 94-132by mixing catechol with various types of amines at weight ratios of60/40 and 40/60 catechol to amine (Cate/Amine Ratio) and varying amountsof 2-ethyl-4-methylimidazoline as the catalyst as shown in Table 18. Theamount of Part A shown in Table 18 below was mixed with about 5 grams ofthe Part B described in Examples 52-58. The OH-Amine/Epoxy ratio wasmaintained at about 0.8. The amount of catalyst based on the totalformulation (%T) and the amount of catalyst based on the reactivespecies (%Cat) are shown with sustained load results in Table 18.

EXAMPLE 248

[0184] The catalyst (2-ethyl-4-methylimidazoline) was added directly to5.8 grams of the Part B described in Examples 1-20. Sustained load testresults are shown in Table 18.

EXAMPLE 249

[0185] A Part A composition was made by combining 4.6 grams of2-ethyl-4-methylimidazoline, 4.1 grams of catechol and 0.5 grams ofresorcinol in a jar, flushing with nitrogen, then capping the jar. Thecomposition was heated in an oven at 121° C. with occasional agitation.After a translucent, homogeneous solution was formed the jar was cooledand 0.2 grams of Printex 3 carbon black was added and mixed with thecomposition to a paste like consistency.

[0186] A Part B composition was made by combining the followingingredients in a cup and hand mixing with a wooden tongue depressor to apaste-like consistency: 46.9 grams of Epon 828, 7.5 grams of MK107, 6.6grams of the epoxy resin premix composition described in Examples 52-58,16.5 grams of Epon™ 58006 resin, 23.1 grams of GP7I silica, 2.0 gramsCab-O-Sil™ TS 720 silica, and 0.8 grams of K37 glass bubbles. To thismixture was added 8.5 grams of catechol and uniformly distributed. Thecup was then capped and heated in the oven at 125° C. with occasionalstirring until the catechol was completely dissolved and the compositionwas mixed to a uniform consistency. The mixture was allowed to cool toambient temperature. An epoxy adhesive was prepared by combining 5.7grams of Part B with 0.5 grams of the Part A in a small ointment can andmixed to a uniform consistency. Sustained load test results are shown inTable 18.

EXAMPLE 250

[0187] Example 250 was prepared as Example 249 except that imidazole wasused as the catalyst and the stoichiometry was 0.92. ComparativeExamples C22-C26 are commercially available and industry accepted one-or two-part epoxy or acrylate adhesives for bonding automotiveapplications. Comparative Example C22 is a structural one-part epoxyadhesive manufactured for Chrysler Corporation under the name MSCD 457Bby Cemedine, U.S.A. Inc. of Oak Creek, Wisconsin, C23 is a structuralone-part epoxy adhesive manufactured for Chrysler Corporation under thename MSCD 457C by PPG Industries of Adrian, Mich., and C24 is astructural one-part epoxy structural adhesive manufactured for GeneralMotors under the name 998-1989 by PPG, C25 is an two-part acrylicstructural adhesive manufactured by Lord Corporation of Erie, Pa., underthe name Versilock™262. TABLE 18 Cate/amine Cat Part A % SLD Ex Amineratio Gms gms % T Cat cycles 232 3-Amino-1-propanol 60/40 33.7 0.77 3.304.87 45 233 3-Amino-1-propanol 40/60 36.1 0.73 3.30 4.89 24 234Ethanolamine 60/40 37 0.71 3.30 4.88 40 235 Ethanolamine 40/60 41 0.653.30 4.90 19 236 2-Ethylhexylamine 60/40 20.1 0.90 2.50 3.66 15 2372-Ethylhexylamine 40/60 19.5 0.93 2.50 3.64 5 238 2-Ethylhexylamine40/60 28.7 0.95 3.50 5.10 33 239 2-(2-Aminoethoxy)ethanol 60/40 21.50.84 2.50 3.67 15 240 2-(2-Aminoethoxy)ethanol 40/60 21.7 0.84 2.50 3.674 241 2-(2-Aminoethoxy)ethanol 40/60 31.9 0.87 3.50 5.13 10 242Tridecylamine 60/40 17.8 1.01 2.50 3.61 20 243 Tridecylaminc 40/60 16.21.12 2.50 3.60 4 244 Tridecylamine 40/60 23.8 1.14 3.50 5.03 34 2453-(1-Methylethoxy)-1- 60/40 20.3 0.89 2.50 3.65 6 propylamine 2463-(1-Methylethoxy)-1- 40/60 20.0 0.91 2.50 3.67 4 propylaminc 2473-(1-Methylethoxy)-1- 40/60 29.3 0.73 3.50 5.11 5 propylamine 248 Noamine NA 0.20 0.20 3.30 4.90 43 249 No amine NA 0.47 0.47 3.75 5.61 30+250 3-Amino-1-propanol 52/39 9.0 0.77 1.20 1.74 34 C22 One-part Epoxy NANA NA NA NA 5 C23 One-part Epoxy NA NA NA NA NA 4 C24 One-part Epoxy NANA NA NA NA 5 C25 Two-part Acrylate NA NA NA NA NA 1

[0188] The data in Table 18 shows how the type and amount of amine andcatalyst influence the durability of the cured adhesive under SustainedLoad cycling conditions. In general, as the amount of amine increases,relative to the amount of catechol, a higher catalyst level may benecessary to achieve extended sustained load durability performance.

[0189] The epoxy resin adhesive composition from Example 248 was testedfor Sustained Load (SLD Cycles) with the different steel and lubecombinations shown in Table 19. TABLE 19 Lube Coating Weight SLD ExSteel Type (g-m⁻²) cycles 248 G60HDES 61MAL 2.70   35 248 G60HDESChempet BW 4.84   45+  248 A40 Galvannealed* 61MAL 4.31   65+  248 A40Galvannealed* Chempet BW 4.84   65+ 

[0190] The data in Table 19 illustrate how the type of metal, the typeof lube and the lube coating weight can influence the sustained loaddurability.

EXAMPLES 251-257

[0191] A part B composition was prepared as in Examples 52-58. A numberof part A catalyst positions were prepared by mixing in jars 100 gramsof each of a variety of amines with varying amounts of2-ethyl-4-methylimidazoline catalyst (Catalyst Grams) as shown in Table20. Only an amine was used as a chain extender in these examples. Theamount of Part A shown in Table 20 (Part A—Grams) was mixed with 5.0grams of the Part B described above. The Amine/Epoxy ratio wasmaintained at 0.82 and the amount of catalyst (%Cat.) is shown based onweight of reactive species. T-Peel Adhesion results at 23° C. on MEKcleaned and 61MAL lubed steel are shown in Table 20. TABLE 20 T-PeelCatalyst Part A % N-cm⁻¹ T-Peel N-cm⁻¹ Ex Amine Grams Grams Cat MEK61MAL 251 3-Amino-1-propanol 40.8 0.66 5.14 137 70 252 Benzylamine 29.70.87 5.07 145 88 253 2-Ethylhexylamine 25.3 1.00 4.97 137 61 254Ethanolamine 49.3 0.57 5.19 128 75 255 2-(2-Aminoethoxy)ethanol 30.20.85 5.04 119 123 256 Tridecylamine 17.7 1.44 4.81 102 61 2573-(1-Methylethoxy)-1- 26.2 0.97 5.00 131 70 propylamine C26 Dodecylamine18.7 1.35 4.82 R R

[0192] The data of Table 20 shows that satisfactory results may beobtained with a chain extender containing only an amine. In general, asthe amine content of the chain extender increases, the ability of theadhesive composition to bond to lubricated surfaces may decrease.

[0193] In the assembly of structures obtaining integrity from theadhesive of the invention, often a structural or frame member iscombined with a panel member. Maintaining the frame and panel in acorrect alignment or position until the adhesive cures is often adifficult task. Often parts are clamped or spot welded to maintain thelocation of the parts. These assembly techniques are often not suitablefor finished panels requiring smooth uninterrupted surfaces free ofdimples or any other surface defects. A self-aligning or positioningfeature has been developed that can be introduced into a frame memberand into a corresponding panel member that fixes the panel member inplace on the frame and maintains its position enabling the adhesive tocure and form a strong structural bond. Such a structure can be seen inthe assembly 60 shown in FIG. 6. Frame members 61 a and 61 b are shown.These members 61 a and 61 b can be separate, attached to othercomponents or can be a unitary part in a frame assembly 61. A panel 62,having two or more flanges 62 a and 62 b, is fixed in place on framemembers 61 a, 61 b. When made of metal (e.g., steel), it is desirablefor the frame members 61 a and 61 b to be hydroformed and panel 62 to bestamped using conventional techniques. An adhesive mass 63 is positionedbetween the panel 62 and each of the frame members 61 a and 61 b. Theadhesive mass 63 can be one of those disclosed herein or any otherstructural adhesive. The dimensions of the panel and members are fixedsuch that a portion 66 of the adhesive mass 63 is wicked into the narrowseparation between each panel flange 62 a and 62 b and the correspondingframe members 61 a and 61 b. The position of the panel 62 with respectto the frame 61 is maintained by positioning means. The positioningmeans keeps the panel 62 and the frame 61 in position at least longenough for the adhesive mass 63 to set or cure. For the adhesivesdisclosed herein, curing of this mass 63 may take up to four hours orlonger. The positioning means can comprise a pressure or friction fitbetween the panel flanges 62 a and 62 b and corresponding frame members61 a and 61 b. The positioning means can also comprise one or more or acombination of channels, dimples or other indentations 64 on one or moreof the frame members 61 a and 61 b with one or more or a combination ofmating ridges, bumps or other protuberances 65 on the correspondingpanel flange 62 a and 62 b. It is also envisioned that the indentations64 could be on the panel 62 and the mating protuberances 65 on the frame61. Alternatively, one or more of the indentations 64 and protuberances65 could be on both the panel 62 and frame 61. Furthermore, anyconventional snap-fit type construction may be suitable for keeping thepanel 62 and frame 61 together. A combination of bothindentations/protuberances and pressure or friction fitting may also bedesirable. Stamping or hydroforming, as applicable, can enable theseindentations 64 and protuberances 65 to be formed as the panel 62 andframe 61 are being formed. It is desirable for the dimensions of theframe 61 and the panel 62 to be selected such that the adhesivepositions indicated by reference numbers 63 and 66 are dimensioned suchthat sufficient adhesive can be used to maintain a joint of structuralintegrity without wasting adhesive. Further, it is desirable for frame61 and panel 62 to be dimensioned so that the adhesive is rapidly wickedinto place in one or, preferably, both of the joint areas indicated byreference numbers 63 and 66. In forming the frame/panel assembly 60, theadhesive can be applied either to the panel 62 or the frame member 61,or to both just prior to assembly. After the adhesive is applied, thepanel 62 is simply installed, and the positioning means locates thepanel in the correct position without substantial effort. The resiliencyof the material (e.g., metal) used to make the panel 62 can be adjustedso as to allow the panel flanges 62 a and 62 b to flex and theprotuberances 65 to snap in place into the corresponding indentations 64of the frame members 61 a and 61 b. This self-positioning feature placesthe panel 62 in the correct alignment and creates the correct geometryfor the adhesive bonds 63 and 66. Whether or not there are indentations64 and protuberances 65 present, the resiliency of the panel materialcan also be adjusted so as to allow the flanges 62 a and 62 b to flexand exert pressure against the corresponding frame members 61 a and 61b.

[0194] Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

We claim:
 1. An epoxy composition comprising: (a) an effective amount ofa chain extender; (b) an effective amount of a catalyst; (c) aneffective amount of a reactive epoxy resin; and (d) an effective amountof a polymeric toughener, wherein the chain extender, the reactive epoxyresin, the catalyst and the toughener are each in an amount and of atype that are effective, when mixed together, to form a thermallycurable adhesive and, when the adhesive is cured, at least about 50% byweight of the epoxy resin is chain extended.
 2. The composition of claim1, wherein the composition is substantially free of a polyfunctionalcuring agent.
 3. The composition of claim 1, wherein the chain extendercomprises at least one of an amine and a phenolic compound in monomericform.
 4. The composition of claim 1, wherein the chain extendercomprises at least one of an amine and a phenolic compound, the amine isat least one of a primary mono-amine, a secondary di-amine and compoundsbased thereon, and the phenolic compound is a dihydric phenoliccompound.
 5. The composition of claim 1, wherein the chain extendercomprises at least one of a catechol, resorcinol and amine compound, andthe chain extender is dissolvable into at least one of the epoxy resinand the catalyst.
 6. The composition of claim 1, wherein the chainextender comprises at least one of an amine and a dihydroxy phenolic,the composition is an adhesive composition comprising a part A and apart B, the part A comprises the catalyst, the part B comprises thereactive epoxy resin, and if the chain extender includes an amine, theamine is only in the part A.
 7. The composition of claim 1, wherein thecomposition is an adhesive composition comprising a part A and a part B,the part A comprises the catalyst, the part B comprises the reactiveepoxy resin, and at least one of part A and part B further comprises thechain extender.
 8. The composition of claim 1, wherein the chainextender is at least one of an amine, catechol and resorcinol compound,the composition is an adhesive composition comprising a part A and apart B, the part A comprises the catalyst, the part B comprises thereactive epoxy resin, and at least one of part A and part B furthercomprises the chain extender.
 9. The composition of claim 1, wherein thechain extender comprises a catechol, the composition is an adhesivecomposition comprising a part A and a part B, the part A comprises thecatalyst, the part B comprises the reactive epoxy resin, and at leastthe part B further comprises a catechol.
 10. The composition of claim 1,wherein the chain extender comprises catechol and resorcinol, thecomposition is an adhesive composition comprising a part A and a part B,the part A comprises the catalyst, the part B comprises the reactiveepoxy resin, at least the part A further comprises the resorcinol, andat least the part B further comprises the catechol.
 11. The compositionof claim 1, wherein at least about 50 wt % of the chain extender iscatechol.
 12. The composition of claim 11, wherein the chain extendercomprises catechol and resorcinol, and up to about 50 wt % of the chainextender is resorcinol.
 13. The composition of claim 12, wherein theamount of chain extender in the composition is in the range of fromabout 8 wt % to about 30 wt %, based on the amount of chain extender andreactive epoxy.
 14. The composition of claim 1, wherein the catalyst isa base and comprises at least one catalyst selected from the groupconsisting of a cyclic amidine, a tertiary amine, substituted analoguesthereof, and a substituted anologue of pyridine, of pyrrolidine and ofpiperidine which do not exhibit enough of an electron withdrawing orstereo chemical effect to prevent the composition, when mixed together,from forming a thermally curable adhesive suitable for structuralbonding.
 15. The composition of claim 1, wherein the catalyst comprisesa first catalyst and a second catalyst different than the first.
 16. Thecomposition of claim 15, wherein the first catalyst comprises animidazoline catalyst and the second catalyst comprises an imidazolecatalyst.
 17. The composition of claim 1, wherein the catalyst comprisesat least one of imidazole, imidazoline, a substituted imidazolecompound, a substituted imidazoline compound,1,4,5,6-tetrahydropyrimidine and a substituted1,4,5,6-tetrahydropyrimidine compound.
 18. The composition of claim 1,wherein the composition is an adhesive composition, the catalystcomprises an imidazoline compound, and the chain extender comprisescatechol.
 19. The composition of claim 1, wherein the reactive epoxyresin comprises a glycidyl ether epoxy compound having more than onereactive epoxy group.
 20. The composition of claim 1, wherein thereactive epoxy resin comprises at least one of an aromatic glycidylether epoxy compound and an aliphatic glycidyl ether epoxy compound,with at least one compound having more than one reactive epoxy group.21. The composition of claim 1 containing an amount of the catalyst inthe range of from about 0.5 wt % to about 10.0 wt %, based on thereactive species in the composition, an amount of the reactive epoxyresin in the range of from about 50 wt-% to about 90 wt-% of theadhesive, based on the reactive species in the composition, and anamount of the polymeric toughener in the range of from about 5 parts toabout 35 parts by weight, based on 100 parts by weight of the reactiveepoxy resin.
 22. The composition of claim 1, wherein the components ofthe composition are present in amounts such that the stoichiometricequivalents ratio of reactive hydrogen sites to reactive epoxy sites isless than about 1.0.
 23. The composition of claim 1, the components ofthe composition are present in amounts such that the stoichiometricequivalents ratio of reactive hydrogen sites to reactive epoxy sites isin the range of about 0.5 to less than about 1.0.
 24. The composition ofclaim 1, wherein the components of the composition are present inamounts such that the stoichiometric equivalents ratio of reactivehydrogen sites to reactive epoxy sites is in the range of about 0.7 toless than about 1.0.
 25. The composition of claim 1, wherein thecomposition is an adhesive that can form an adhesive bond having animpact peel strength of at least 3 J at a temperature in the range offrom about −40° C. to about +90° C.
 26. The composition of claim 1,wherein the composition is an adhesive capable of forming an adhesivebond having a T-peel strength of greater than about 85 N/cm at 23° C.27. A structure comprising a first surface and a second surface joinedby an adhesive bond, the adhesive bond comprising a cured mass of thecomposition of claim
 1. 28. The structure of claim 27, wherein the firstsurface and the second surface each comprises at least one materialselected from the group of materials consisting of thermoplasticpolymers, thermoset polymers, reinforced thermoplastic composites,reinforced thermoset composites, metals, metal alloys and combinationsthereof.
 29. The structure of claim 27, wherein the structure comprisesat least a portion of a vehicle.
 30. The structure of claim 27, whereinthe structure comprises a joint having a welded bond in addition to theadhesive bond.
 31. The structure of claim 30, wherein the welded bond isformed through the adhesive bond.
 32. A method of assembling thestructure of claim 27 comprising the steps of: (a) applying an uncuredmass of the composition of claim 1 to at least one of a first member anda second member; (b) sandwiching the uncured mass between the firstmember and the second member; and (c) curing the composition to form anadhesive bond so as to adhere the first member and the second membertogether.
 33. The method of claim 32, wherein the first member is aframe member and the second member is a sheet-like member.
 34. Themethod of claim 33 further comprising the step of welding the sheet-likemember to the frame member through the uncured mass before the curingstep.
 35. The method of claim 32, wherein the first member is a framemember and the second member is another frame member.